If you have a tank that size how about insted of dividing the tank to half water half eartn you could insted do mostly earth with an oversized water accessory like these Rock Planters :
Average size 20"x12"x6" deep. Table Top models are smaller.
Maybe you could find something like this locally or contact stone art about shipping possibilities, they ahev USA and Canadian locations listed on their site. Or if you're crafty maybe you could even make something like this yourself using suitable amphibian friendly materials. You can simply remove the water feature for cleaning or get a small pump, even use a shop vacuum (a wet/dry vacuum) to drain water and clean if it's too heavy to lift. I would love to get one for my son's ball python's tank.