Housebroken dog urinating constantly inside & hard to walk

Question
I'm a student living off campus at a two story house with five roommates. My roommate Steve adopted a 2 yr old yellow lab named Mac (supposedly pure bred but is almost 90 lbs and has a very long face and very long legs) in late December. He was in an abusive home, and then part of a rescue program, the family that adopted him had him a month but asked Mac's breeder to find another family. The breeder contacted my roommate (who was looking for a dog, and Steve's family has dogs from this breeder).

Steve works or is in class almost all day, but walks the dog morning, late afternoon, and late night before bed, I or another roommate usually walk the dog at some point during the day, and he's played with in the house at night when not at class.

But the dog is very difficult to walk because he constantly pulls no matter how we try to get him to walk next to us. He has so much energy he pulled away in a park once, and just took off, didn't respond to his name at all. Because its winter and icy out, its very hard for me to take him out for a walk (more then the boys), and theres no yard he can just be let loose in. I would take him out during the day if I could walk him easier.

The house smells like urine constantly, everything is covered in dog hair (even though I try to keep him out of my room), and the dog will eat and tear into our food if no one's around, but is very well behaved and quiet if someone nearby. If someone shouts in the house, or calls to him loudly he starts to pee, if you say 'stay' or another command loudly, he'll start to pee, so its impossible to verbally reprimand him for peeing because he'll run around the house peeing and leave a trail upstairs and down. He's pooped in the house several times too.

Yesterday Steve was at class and his dog started urinating on the carpet, another roommate ran to grab the leash and the dogs collar and he bolted past him and out the door and disappeared in a matter of seconds. We didn't find him for two hours when we got a phone call from a dorm hall on the other side of a cemetery from us, that Mac had shown up over there.

Is the dog not being walked enough, and is there anyway to correct the leash behavior? Raising your voice above soft while talking to him is enough to get him to urinate, and the other day, while a roommate was rubbing his belly, the dog just started peeing. Any chance of something medically wrong?

Thank you for any help!!

Answer
Christie, Hi! Okay regarding the peeing when shouted at or belly rubbed, it is normal for a dog who has been abused in the past. He is extremely insecure and you are definately not going to make life any beeter for him by screaming at him!! So the only answer is to always talk to him very gently and the only reason why he seems to pee in the house is because his timings are not regularized. Fix 5-6 timings for him to be taken out and do not deviate from them. Mind you the night gap must not be more than 8hrs. Leash behaviour: What I am going to say now needs to be followed with great caution or it could prove fatal. Go to your local pet shop and purchase a large check chain. Once purchased please do not hesitate to ask the shop owners the exact method of using it/putting it on. I'll tell you the most important thing though: 1.Always make sure you put on the chain right and  2.whenever you pull on it, pull with slight short jerks and never keep the chin pulled, that could strangle the dog easily. Just remember that the 2nd point will not hold good unless you follow the 1st point.
The check chain will take care of the pulling.
Also he pees all the time because he is nervous. You will have to give him lots of love and care.
regards-Ardesh