If you want to do it in Hammer, the only reliable way I can think of is to use teleport meshes and disable the mesh behind the gate. People with large playspaces can just walk through.

The other option is writng a script, although that's very limited and tricky to integrate into the map. The player class has a AllowTeleportFromHand function that lets you disable the teleport from each hand. Note that some of the tools players can spawn will also use this function, so the teleport will reenable once they drop the tool.

What about a large box trigger behind the gate that would call a function to set the player's position to a point in front of the gate? That way, the player couldn't even walk through without being automatically teleported back. Unlocking the gate would disable the trigger. You could use Rectus's player teleporter function from this guide.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=756119531

Thanks so much for the info, I'll give those a shot and report back