I think trainers can help in any area.
I think he is peeing/pooping in the play/garden area just because he smells the other dogs. Is it not allowed to do it in that area ? If it is allowed as long as you clean up after him , then I don't think it would be a problem .
If it's not allowed maybe taking him for a walk before the garden area would help. Or maybe you could try taking a pee pad with you and letting him go on it in the garden area, if anything it may just reinforce the pad training at home.
Good luck |