Hi Jill! I know, this one is a real toughy! It takes lots of drilling to get the legs even. I would suggest ground drilling it, and also- watching the legs as much as possible as you lower them, at first as it gets easier. In terms of the back arch- yes also very tough! Try beginning as the legs are lowering with a short arm grip, then once the legs are through the loops, bend legs as much as possible and switch to a longer arm grip. Reach as far as possible over your head, and arch like crazy. Give this a few whirls. Also- timing is a factor. If you can begin the arch back as soon as the legs are throughout the loops this will help. Let us know how it goes!
