In our house, we had a mouse problem when we first purchased it. One bathroom started smelling awful. For over 3 years it continued to smell like a dead mouse urine smell. By now, we had successfully ridded the house of mice. (Between traps, a cat, and plugging holes.).
Well, the time came to remodel that end of the house. Out came one wall to make room for a bigger bathroom, and there it was ... a dead mouse, all shriveled up. Quite obvious, he got into the Decon I set out years earlier.
Lesson learned. Never poison them. Trap them or let the cat get them.
FYI, got the dead rodent out and all the wall attached to it, and have never had mice again, and never the smell again.
Moral of the story? If you have a dead mouse in the wall, you'll never get rid of the smell. If you have urine in the walls, ceiling, or under the floor, you'll never get rid of the smell. Cover it, mask it, fumigate it, it will still be there unless you can physically remove everything that touched the urine or the dead mouse.