A camera...catch him in the act and take a snap or make a video; these days you can do either with a mobile. Or, pour red pepper all over the top ones so that when he grabs them he'll either sneeze or get it in his eyes? (Just brainstorming, here.:-)

Borrow a dog that will bark and sound very scary.

Tie the pile together by running a loop around the end of each log, then tie it to the house via a railing or something.

Do you have any kind of fencing that could be put up with a lock and key?

Seems pretty cheeky to be so bold!