This admin ablity to move other players around is from ULX not prop protection. It's supposed to be there. If they are abusing the powers, you will have to disable access to the slap command. To do this per user, type ulx userdeny "ulx slap" in console. You can not use this command from the game console for superadmins, you must do it from the server console.
To disable it for all admins, goto /garrysmod/data/ulib/groups.txt
"out"{
"admin"
{
"deny"
{
"1" "ulx slap"
}
}
}