If you glue the vinyl down, and either run it under the walls (during construction), or put molding around the edges, nothing is going to get underneath. I say this is a good reason to glue it down, as the pieces I have used without glue, like for the nestbox, have been a PITA and I eventually threw them out. If for SOME reason you need to redo the floor (I can't imagine why, as they never touch it with 4 inches of litter on top of it) you can simply do it like contractors do--emboss over the top to fill any holes, and glue another sheet right on top of that. If done properly the glue is almost dry when the vinyl is installed, and very soon there is no odor at all.