Hey I have a question. I'm about 20 hrs into the game [currently up against a wall with the Anor Bosses and have no humanity left :(] but I am thinking of heading back and revisiting the Undead Asylum. I tried it before I left for Anor but just kept getting raped by the fire demon guy. I also have the guide for the game and it suggests bringing a 100% fireproof shield to cancel out all damage he does [with his fire attacks of course]. But there is no shield in the game that is 100% FP. So my question is about upgrading/reinforcing shields. I'm a little confused on how that works. I get weapons but not shields. Is there a way to bump up different ele up on shields to full 100%? I look at the stats on different upgraded shields but +5 or +10 different ele are still not 100%. Any help? Thanks

I'm fairly sure that the Stray Demon is magic damage not fire, regardless the Dragon Crest Shield can be found next to the undead dragon in Valley of the Drakes, take the elevator down from where the Firekeeper is in firelink and then turn right into a similar tower to the one you come out of, at the top of the stairs is a door, if you have the master key you can open it and take the wooden plank over to the other side, then go left along of the cliff and over another bridge, the dragon is asleep and will wake up when you either loot the items next to it or attack it, it's pretty easy to loot then roll back the way you came to avoid it, if you don't have the master key you need to go to Darkroot Garden and get down to where the Bacl Knight is (next to the stamina regen shield) and there is a cave which takes you to the valley from the other end.

Regardless, you need to dodge that attack by staying to the side (i suggest running around to the right all the time), get behind him and wail on him.

The only real use to upgrading shields, as far as I can tell, is the increase in stability. Basically, the higher the stability, the less stamina you lose per blocked attack. I don't think there's any way of upgrading the deflection percentages, but my personal experience was with the silver knight shield, which takes the twinkling titanite upgrade...so maybe the other paths do different things. I should go check that out myself now.

His "fire" damage is actually magic damage so a shield with high magic blocking is wanted.  I used the Crest Shield as you can find it in the Undead Asylum on your return visit (you get it from killing that guy who originally gave you estus). 
Don't worry about upgrading the Crest Shield unless you plan on using it as your main game shield (and I wouldn't simply because it upgraded with twinkling titanite) To answer your question, upgrading a shield doesn't usually increase any of its resistances, whatever the basic shield blocks, the shield +10 or +15 will also block, no more and no less.  What it does improve is the shields stability rating.  It is usually better to upgrade your weapons before upgrading your shield because this improvement is only slightly noticeable while improved weapons make a huge difference, however, the importance of an upgraded shield should not be neglected later in the game.  Basically stability means each hit drains less stamina so you can take more hits before getting staggered.
 
So in your case, I'd grab the Crest Shield and don't worry about upgrading it, the basic version will serve you fine against the Stray Demon.  Just keep circling it, backing away with shield up when his magic fire attack comes, and make sure to always stay behind him.  If you do this he'll keep a consistent pattern of waddling around trying to get you in front of him, then fireblasting.  As long as he keeps doing that the boss fight is manageable.

Sounds good. Now I get the fun long trek back to the firelink shrine to head to the asylum. I'm trying to take the demon down to get the doll that will allow me to go to the painted world. My ultimate goal is to get the red soapstone so I can invade people when ever I run out of humanity and have no other option. That's where I am now, stuck in Anor with no humanity to summon people to help with the bosses.

Umm, you don't have to fight the demon at all to get the doll. Just walk around the edges of the area where the asylum demon was and you won't fall into his lair. Then just head back to your cell the same way went when you were in the tutorial. The only enemy that poses any threat in your way will be one of the knights you first meet when you get to Anor Londo. If you're already on the bosses there he should be more than manageable for you.

@Barrabas said:

Umm, you don't have to fight the demon at all to get the doll. Just walk around the edges of the area where the asylum demon was and you won't fall into his lair. Then just head back to your cell the same way went when you were in the tutorial. The only enemy that poses any threat in your way will be one of the knights you first meet when you get to Anor Londo. If you're already on the bosses there he should be more than manageable for you.

>.> wish I would of known that when I was there hehe. Yay for crazy amounts of backtracking.

I know this is a tad old but I just beat that stray demon thing the other day. 
Just another tip for him really: I found it best to just always stay behind him and back up when ever he points his mace down. And of course make sure you block in case he swings. He seems to spam that magic explosion though. He can't seem to hit you if you're always behind him, so he will often do the down ward explosion in which case just back up if he starts pointing the mace down then go back after the red aura of the attack clears. He will try to butt stomp sometimes too so when he flys up just back up and when he lands just circle back to behind him again (it takes him a good 3 seconds or so for him to stand back up).  
He's pretty easy if you stay behind him =) 
I did lose a fair amount of souls figuring it out, but once I did he was cake.

Ya I got him down after a few tries :D Now I just need to figure out which sword aside from the Drake Sword am I going to use. Leaning toward Uchigatana since I've used it before and loved it. Was thinking of going lightning with it but the bosses in Anor are lightning so not sure if thats a good idea.

I'll piggyback your topic with another shield question:

Right now I'm using the Blood Shield. Seems like it has pretty good defense, and I like the resistance upgrade it provides. What late-game shields do you guys use? I put +2 into mine because the stability seems pretty low, and it didn't cost too much. Any other shields I should be looking for? Looking at the wiki, the Paladin shield seems amazing.