Mr. Meis is right. Although drilling holes in the foil won't add stress, it is taking away strength from the very centre of the foil, where the most stress occurs.

I've seen foils fold, it's not pretty. The mast comes down at the very least. And I'd hazard a guess that if you had a big load on the foil at collapse, you might even break bows as they're pulled inward.

There are clips available, or you could fabricate something, or even duct tape, but for me, I wouldn't drill my foil...

sea ya
tami