When planing across the grain your end vise should still hold…mine does not. The vise was a freebie from my Grandfather and the machining is very sloppy, do not buy a vise like this, it will irritate you immensely.
But if you happen to have one, and your work keeps popping out of your dogs, two finish nails can solve your problem. Just make sure they are low enough to avoid your plane blade.
Sometimes having an ugly bench is a great thing.
-- Make furniture that lasts as long as the tree - Ryan