Some say that cats mark out their territory by leaving their pungent poop/urine where it counts, as they see it. So you could acknowledge kitty's need for this by leaving toys or treats where it counts and talking gently to kitty about things. "Bit too smelly for us..."..."Hey, it's your home too, but..." ..."We love you and..." Give kitty time to settle in, might be a while, like humans need, to relax in a new home. Months, not days, in my case, for example.
I swear our cat gets the gist of what we are saying. Confirm this by watching kitty's eyes and facial expression. Either/or.