How do you keep the back of the dovetail from blowing out when you are chopping out the waste. I've finally gotten to the point where the dovetails fit fairly well, but I'm getting chip out on the back side.

One other thing, there was an article in Fine Woodworking about clamping several drawer sides down at once, kinda like a stair step, and chopping out the dovetails on all of them without having to move and reclamp them. How do you keep from marking up the drawer slides with chisel marks?