need advice on triggers & counters

[Someone Else's Problem]

so here's the thing. i've got an area of eight squares with four monsters on it. the idea is that once all four monsters are dead, a pit in front of the area closes and the party is able to cross over. my original (and ill-conceived) plan was to have the pit closed by default and put a trigger on each tile in the area (activate by monster, constant weight only, target pit (activate)). this made good sense to me, but RTC made it pretty clear that this wasn't acceptable when i tried to compile it. guess this is a "multiple simultaneous instructions to the same object" problem.

so, i'm guessing that i'm barking up more or less the right tree, but need to use a counter, but i'm not all that clear about how counters work. i'm assuming that i need to have the triggers as before but pointing to a counter with a count of 4; the counter activates the pit, so when the count gets to 0, it should do the opposite and deactivate. is this the way to go about it? any advice would be appreciated.

[linflas]

have a look at the counter used for the Ful Ya Pit in CSB... maybe it could help

[Someone Else's Problem]

the counter for the fulya pit counts four corbamites and activates a teleporter when it gets to four. this much i understand about counters. the problem here is that i'm trying to get a constant input to the counter from multiple triggers. i am assuming that if every square that the creatures step on is of the "activate:constant weight" variety then each time a creature steps off one trigger and onto another one you get a deactivate and activate sent to the counter and the value stays constant. if one of the creatures is killed, then there's one less activate being sent and so the count goes down by one. if the count gets to zero and the counter is set to activate the pit, then it should deactivate it and close the pit. i am also assuming that if the counter is between zero and its count value, then it will not send its output.

hmmm. looks like i've talked my way through it. i'd still like to know if any of my assumptions are wrong and whether there's a fiendishly cunning way of doing this, though.