On the PP and Tib fac there is a place that you can set a beacon and it would be very hard to disarm it... its also very hard to get to there(its reched on foot)On the PP I have be shot down in my Apache when above the tube on the PP and fallen inside with my beacon but you need a timed mine to get out.
On the Wep fac I like to stick a beacon right at the top to make the eng walk long.. then when he tryed to disarm it thetimed C4 blows up in is face and he has to do it all over again just to find he is too late