[B.T.]

I usually use two maps:
1. the "gaming board", that everyone can see,
2. my personal sketch, that is hidden somewhere in the chaos behind my GM screen. I erase and work with a pencil on that sketch all of the time.

When we work with a board (as many of you, I use a "battle map" with an imprinted square-grid - I draw on it with "non-permanent markers"), I usually remove the tokens/miniatures for NPCs, that can not be seen by the players (Or I make shure, that the players know: These handfull of soldiers went into that house, but, off course, they don't know, if there are more evil-doers in the house, or not!).
Sometimes this is time consuming, because you relocate some of the miniature all of the time.
On the other hand: I want my players to enjoy gaming. Therefore I don't mind, that some things are a little simplified. In this case: The players can see, how many miniatures of Soviets have been removed.

I don't place miniatures for enemies, that have not been reckoned by the players. If, for example, a group of several enemies fire through a hole in a wall or a window, I dont tell the players, how many guys are behind that wall. And I make my rolls "hidden", what means: no one can see, what modifieres work. Those 3 bursts and 4 single shots could come from 2 fiends, or 7 fiends - my players don't know for shure!

In my group, this is seldom the case, but if the group splits in two parts with no line of sight, I split the group in two teams, actually sitting in different rooms. If someone fires into a direction, where he can not see a comrade of the other team, it is possible for them to hit one of their group members from the other team. Again time consuming, but it adds some tension to the play and is a permanent reminder, that the PCs communicate with one another.