Love the leg vise! Yeah, I've had to have benches on casters before for the same reason. Even locking casters want to slide around on smooth concrete. I ended up making some big blocks for each corner that I could slide under the lower crossmembers to elevate the bench just enough to get the wheels off the floor. That only works if your bench is light enough that you can lift each corner, though.
That bench looks like it's seen a few projects. I like the way well-used workbenches tell a story about all the projects they've been involved with.