Polo Rules

In my head it'd be pretty easy to achieve:

If you have two stationary players within the masked area then the ref would warn the players "one of you needs to leave the D", if they failed to do that then you'd stop the game and ask the player to leave the D and that if they did it again they'd be ejected for 30 seconds

Ok, stationary, good, that makes it much better.

You'll still need to word it carefully to avoid ways around the spirit of the rule.

Is hopping on the spot stationary?
Is track standing (with a bit of back and forward) stationary?
Is rolling back and forward around a tripod stationary?