Arca plate advice needed

I picked up a gimbal head to use with my new 400mm f5.6. The Arca-type mounting plate has one screw and mounts fine to the tripod collar. But the camera/lens combo will turn on the plate despite having the screw as tight as I dare tighten it. I've seen other plates with two screws, but the tripod collar only has one screw hole. Sorry for being a dunce on this, but how do you secure an Arca plate to a tripod ring so it won't turn?

EDIT: I was just reading Bryan's Wimberley P20 plate review and he says it has some nubs to keep the plate from twisting. So now the question becomes which plate for the 400 f5.6?

EDIT-II: Looks like the P-20 fits the 400 5.6. On its way from B&H :cool:

(You've just witnessed the learning process in action.) ;)

Mark....at least you kept your learning to a single post....I had a whole multi-page thread running on tripods, ballheads and arca-swiss plates where I was learning as I went....:)

But, yep, sounds like you found it. A lot of plates have edges that prevent the twisting. I had a few pictures of the RRS plates I bought on page 4. FYI, Really Right Stuff let's you select plates by lens for Canon. Here is theirs for the 400 f/5.6.

I have several Wimberley P-20 plates, they work well.