I don't know whether its because I walk in a funny way, but I'm always finding that the back strap on sandals slides down my heel. I tend to find this out after I've bought the sandals, and I then find them really unstable and hard to walk any distance in. As a result, I only have one pair of sandals I can really walk in, and they're Teva flatform, with their nicely adjustable fabric straps. Has anyone found a solution for this or am I alone in my slidey-ness?? I suppose I could shift to sandals with ankle straps, but I've got quite chunky calves, so I don't think it would be a great look.