Last time I made a TDM, the spawn rooms lead directly onto a corridor whilst only being separated by a door. Anyone who came out of the spawn room would probably be killed instantly without having a chance to react, and people could just walk in after anyway.
Teleportation is something I thought would work, but there's still the issue whereby anyone teleporting to location A can be killed instantly be anyone who happens to be there already, and the same in location B, C, D, and so on, even if the teleports are random or player chosen.
Any ideas?