Our lab mix lump is an un-neutered adolescent dog that alone sounds bad enough. He has been house trained for quite some time, for about two weeks now he has been peeing inside after being taken out he does sit at the door and wait to be taken out but doesn't do his business there. There is a new dog that has moved in next door but my neighborhood has a lot of pets and strays running around so I don't know if the new dog is the problem. There have been no other changes that I can think of and we don't go on long trips. He isn't sick ether so if anyone could give me a clue as to why he's doing this I'd greatly appreciate it.

If he isn't neutered he may be marking his territory. My male Pomeranian isn't neutered either and he is a big "marker". He knows after some training that he shouldn't be marking in the house... you basically need to start from scratch with the potty training, lots of praise & maybe some treats when he goes out... a firm NO when you catch him in the act, then quickly take him out to where you'd like him to go. Getting him neutered may also help your cause... makes them not want to mark as much!