You hard-core light travelers (I'm not one of those...I'll pack beer sometimes) are NOT going to like this idea.  I use an old window sash weight.  It has a eye hole to tie or carabiner a rope to, it is skinny and can slide into a pack very nicely, and the weight (2-4#) is just right for holding a canoe.  My partner hates this idea, but I'm the one carrying it.  I don't bring lots of clothes anymore, I found I just didn't wear them.  The reason I don't use a mesh anchor with rocks is sometimes they get stuck between rocks, and it takes some pulling to get it out.  The thin anchor I use is great for mud, rocks and weeds.