I did my 55 G FBT tank with 60% water & 40% land. I made a separator with a piece of acrylic which I purchased at Home Depot. It's quite easy to cut to size--just score it & hold the scored line against a square edge, like a countertop or such. Then just snap it. I secured it in position and made it water tight with aquarium safe silicon.

However, I am now in the process of redoing the whole tank. I found that they prefer the water side with stones for climbing and hiding. Also, they really made a mess with the land side--always getting the soil etc into the water. I'm redoing it and it will be all water, with a stone climbing wall and other 'islands' of stones and a fake log for a hide. They also like plants for hiding (and destroying) I started using plants without soil a while ago & found that there are several types that do well in the water alone. I root them in water, then put them directly in the tank, using some stones to hold them up in place and to protect the roots and to keep the frogs from getting tangled in the roots.

I'm close to finishing, I'll post some pics when I finish.