Excellent idea, but yes, tricky.
Have a wee background script checking if any links in the fence have been damaged ... if they have the BMP gets a doMove command. Also check other likely targets such as petrol station. And every guard.
Similarly, if there was some way you could name the satchel charges, you would be able to tell if one had gone off ..... possible in Resy?
I don't know if its possible to check the behaviour mode of a unit, but if it is you could get all the guards to head towards the dude who has just gone "aware" because he saw or heard something.
Background script checking if there has been a change in each player's ammo state: if there is then something must be happening => guard domove getpos player.
(That's enough stupid ideas - Ed.)
Sentry WPs are no good to you here. To be fair, if you have a bunch of guards whose wayponts are move-move-cycle-guard and you synchro a switch trigger (west detected by east) to the cycle WP it would help. The dudes will set off for your guys as soon as they are detected. Doesn't work if there's just an explosion though, which is of course the root of the question, but I'd still consider putting it in as a backup and for when all hell really does break loose.