You've potty trained him but now you've moved, so now he's marking his territory all over again and besides, as much as you love him, his place is outside and he is not going to run to the pot every time he needs a leak.

First...when you take him out on the lead...stand with him...UNTIL he goes. It may take awhile and patience is the key. DO NOT COME BACK INDOORS UNTIL HE GOES! You know he has to go...so take the time and stay out there with him. This is not a play time...just stand with him in the yard...when he finally does go, praise the heck out of him and then come in. He has to learn the difference between play time and peeing time. Keep giving him a command to go...ie with my dogs, the command is "go". And they do, each and every time. Next, be sure you are cleaning the spots in the house where he has gone very well. Use some type of an enzyme cleaner such as Stink Free...(or any enzyme cleaner sold in most pet stores)you may think you have cleaned well, but the pooch's nose is very sensitive and can detect the least little odor...he may try and remark the spot. At 3 months, he is still yet a baby and you wouldn't expect a 5 month old to be potty trained. It is physically impossible. So, patience. Crate training is a great way to contain them at night or when you can not be with them. Dogs will usually not soil where they sleep. Also...with hold the water after 7pm or so, this will help him get thru the night...

Source: www.city-data.com

Get yourself from Amazon dvd's from Cezar Mullan(?) he is a world renowned dog trainer and dog psychologist. Amazing stuff this guy can get dogs to do. His favorite dog is a pit-bull and its so well trained that he uses it when he wants owners of aggressive dogs to see and realize that any dog can be trained. He calls it dog-training for dog owners.

Watch the "Dog wisperer" on TV. You'll see all the things and tricks you need.