No need to worry about sealing the top for the salamanders, they are lousy climbers. This particular type of salamander is a mole salamander, so they should spend most of their time in the terrestrial portion. I would make as much of the tank terrestrial as possible. This means however, that they spend a lot of time out of site, so students might find that sort of disappointing. You'll need to consider a feeding site of sometype as well.