I fiddled with the legs, tried reversing them, pushing them in further, etc and I did notice that some of the legs have a much tighter fit than others, but not all of them. I'm sure if I got 3 or 4 tight ones on each platform it would help considerably, but I've got 4 of these things going so I'll probably just use zip ties or fishing line.
I used some retaining wall blocks to weigh them down, but I remove them after swimming. I am concerned that their porousness offers too many hiding spots for algae, so I will either paint them with an epoxy paint or, more likely, fill bleach bottles with quickrete and see if that does the trick.
Overall though, these work great!