Rust Prevent TPing outside of map

So I've recently discovered a really bit issue on all modded servers with the option to TP home and to friends. People can swim for 30 minutes to get around 20k meters away from the map and dive deep down into the water and build up from there on. I need something to be able to prevent players from doing that while still having the TP option to be a thing. Any ideas?

 

Pretty sure a simple plugin could just block building if player Y coordinate is less than 0.

Actually, looks like this plugin will do it.
NoWaterBuild for Rust | Oxide
Maybe just set the depth to a few meters or more, so people can still build in lakes and shallow areas.