Multiple Monster tokens and Initiative

For years I have always rolled one initiative for a group of monsters when DMing.  I throw a bunch of tokens out, pick one, and roll Init for the group.  I tend to forget which one I rolled Init with and delete the monsters when they die.  I often end up deleting the one that I rolled init with.   Doh! Are there any tricks to avoid doing this? I guess I could spawn a token off the map that they can't see and use that to roll Init.   Any other suggestions?  Just curious.

Put a marker, like the red dot, on the monster you rolled initiative for. Or put one of them off to the side that's not part of the first and you roll initiative for

Roll once for all of them, but add them all to initiative

The token marker is a good idea.  That or put one more mob down than you intend to use and have the extra one off to the side.  I usually move dead mobs off to the side rather than delete them.  That would work as well.

Thanks guys!  I think having a "init" monster off the board (in the walls) that will roll Init is the best way.