Good fins should drive themselves onto the foot, and the best ones only have a strap because we expect it! Force fins, which are very expensive and very popular in some diving groups do not need straps, and work well, but i would not recommend them for tubing as they are too expensive.
I have discovered a new boot that may be perfect for all our needs, wading, tubing and summer wading without waders. They are cheap, very durable and both Mike and Hamish think they could be ideal. They were designed for sailing and surfing I would imagine but are real tough, well made, and look kind of like light weight wading boots or canvas trainers, but are neoprene lined and front lacing. They are only £29.99 retail but i will be working on a deal price and will post a picture and discounted price here tomorrow night
D