I think they should look at blizzard for some inspiration on mines...
in starcraft, a unit has the ability to lay mines. however, when there laid, they are indeed burrowed into the ground... and they dont move untill someone gets too close... and if someone moves too far away, they just re-burrow themselves...
i think something along those lines would be good...
if not, then just add good old proximity (sp?) mines like the good ol' days of golden eye 007... (stick em to the wall, if someone gets too close... POW)
i admit the spider mines as of right now kinda suck... but i play more ctf than ons... and the only time i see mines is in vctf...
tho some people do just abuse it... they'll sit behind a hill and toss em over just to try and rack up frags... i think that's something that they should get away from... u should have to arm them yourself or somethin.