I've been looking for a good example of wedging up, leave it to Harry! Yesterday I took a piece of scrap from planing practice and cut it down to 3 1/4" x 18", then ripped it diagonally and jointed the edge.
I picked that width because it's the spacing between my dog holes plus the flat on my Veritas dog, so that's the max width I'll ever need to wedge (could also just use shorter wedges and drive the end of one past the other). I picked that length because it gave me a long, narrow taper.
I ended up cutting one of the wedges in half, since most of the time the width I need is big enough that I can just use the front half of the wedge with it's back half, as in the first picture below.
These hold great! Just set the right wedge in place against the dog, then hold it down while driving in the left wedge to the desired amount of clamping pressure. The flat on the narrow end gives you a place to set a piece of scrap to knock it apart.