You just make a trigger that has this in the on activation..
[this] exec "noexit.sqs"
Huge, and a rectangle.. OVer the whole outside of the map, inland a fair bit.. So you can't see the edges..
And save the noexit.sqs script with this in it..
_unit = _this select 0
HINT "You have left the mission area"
_unit setdammage 1
You could have another trigger, a bit bigger than the other one.. So the players activate it before the "kill-me" one, onavtivation feidl
HINT "You are leaving the mission area, turn back"
Gd luck
The setvelocity idea.. It would be fairly possible.. But they would get kileld
- Ben
PS, will write a better version tomorrow