Dog Peeing in the House?

We have 2 Cocker Spaniels 4yr and 8, a Boston Terrier 6yrs, and a Border Collie 11/2yrs. We have had issues with the Boston Terrier marking the bed and some furniture, but all has been good for a long time. We went away on vacation and when we came back we are finding one or more of them are peeing around the house. We don't think it's the Boston as he is ususlly with us. We think it's one of the Cocker Spaniels or the Border Collie. It happens when we are not looking and we usually find it by steping in it. Any suggestions?

By Don