Bacon fat should be a good bait additive. Its odour travels well and it is a nice greasy treat. I used cheese and peanut butter mixed together and tied to the trip lever mostly.

What really bothered me is the live trap failure. I thought they should work but never produced any results. We by the way have farms in our vicinity and about every ten years get some rats in the house.

Some attempt can be made to deny them access but it can be quite a job to do sometimes. They can climb brick and get in through very small places. Or on occasion will make there own access portals. Too bad you have not identified what you actually have yet. If it where rats I would suspect they would be working their way to the lower levels for food alone. Then again geographically there are different specis of them with possible different behavior profiles.