I have the falpro goodwood and really like it, but again no back leg straps, it has never moved though. The only one I can think of with back leg straps is the masta I think climatemasta? My friend has one it has a fixed neck though and the liners are slightly more fiddly to put in, but then are part of the rug so no extra straps. Or possibly look at the bucas select which I think has leg straps, but does work out quite pricey
The climatemasta we had at work didn't self right. It had cotton liners and lining rather than satin and if the horse rolled or shook it stayed wonky. Did have leg straps though.