From Worms Knowledge Base
When activated, this mine-like device blocks any teleport activity within it's range. The device remains active indefinitely until destroyed, and until then neither objects or worms, friend or foe, can teleport into the area near the Teleport Block. If such a teleport is attempted, the object or worm is teleported to the edge of the teleport-proof area. A thin pulsating glow of a circle would define the area of activity of the Teleport Block.
This should require little programming. The range would be decided probably by the power setting of the weapon and a circle of the landscape defined by that and it's location. Then it's a case of the game engine 'noticing' an attempted teleport there and redirecting it.
Useful for keeping enclosed areas enemy-free, and protecting territories from easy invasion. Most importantly, it would prevent the notorious teleportation of a mine directly to your worms side, assuming both this and the Object Teleport co-exist. Not so useful for preventing the Object Teleport from teleporting an Anvil high above, though.
Having to cope with not teleporting your own worms to the area should be easy but the slight disadvantage that comes with this weapon is that no crates will teleport to the area either.
This would balance out the powerful Object Teleport which lets mines be teleported straight next to you, but even in a game without this weapon the Teleport Block can be useful, especially with the Super Teleport about.
(Note: an alternative version of this device is in the form of a girder, which prevents any teleports where the girder lies between origin and destination. The subtle difference between proximity inhibition and line-of-sight inhibition makes the variations very different strategically, and perhaps both could be included as seperate weapons.)