It's a security vs vulnerability thing. If you have enough 3d features in there for them to kind of feel like they my be tucked in someplace you might be able to get by with four open sides. Like 6-8 inch tall logs laid out in an H pattern in your tank or two stumps with a log fallen between them. 0-0. That way if you're the frog you feel like there are three sides covered but the tank is 360 visible. And the frogs could climb up over the top to go from side to side as a short cut.
A second idea is to place walls separating the tank into four different tanks, each with its own pane of glass of the big tank as a viewing point. It would a allow for keeping a variety instead of just one species. One con is that if this thing is too tall to look over, you've just cut everyone's view of other ppl at the table.
Just some ideas.