Limit their freedom to where you can supervise -- perhaps one room. Do not increase their freedom until their potty habits improve.
Eliminating the scent in their accident spots is also crucial.
While positive reinforcement is definitely the way to go, you can also give a gentle "uh uh uh" or "oh no" when you catch them going in the house.
How old are they and are they spayed/neutered?
__________________ Kristin, Max and Teddy  |