Regions? Grid? WTF?!

Well, I'm making a mini-board-game and a feature that i'd like to implent into my map is that when you are out of eh, dots on the dice, moves to make, whatever(cant find the word).And you have ended up on the same square as an enemy player, his little guy will be wiped out of the arena.

So, basically, what I'm looking for is an event. Now i cant figure out what event i should use to fire the trigger, and you have to base the whole system on that single event.

Now the idea i've got so far is that collision is turned of for all players and regions are assigned to each of the players units via a region array and by the end of each turn they move to the unit and if they detect another unit in it it will move it back to it's starting point.

I also had an idea about a gridsystem, like. But i have no idea whatsoever of how to create such a system, now i know that such a system would help a LOT in this map as it would not just make this part easy, it would allow much more precise and exact movement...

Now, is anyone of you willing to tell me if this possibly could work or even better, tell me how (or point to a tutorial) about how you make a grid system. i saw a weekly map channlenge about making a snake game but i cant find it again as thoose maps most likely would contain such a system.

Thanks in advance - MilkmaN

btw, you have to be able to detect which player who is knocked out.