I haven't had a problem with my cat hanging out in the RR room, ie garage. He as a younger cat, would jump up on the layout during some construction, but when he pushed a heavy Bowser ex-PRR K4 4-6-2, with many extra brass details applied, to the floor from its perch over a distance of 5', I decided to fight back. I filled a spray bottle with water, and anytime I caught him on the layout, he got wet.
He no longer gets on the layout, but loves to come down and share a chair, or sit in his own, and watch me work. This is allowed.