What do you have?

[NSABill]

I am probably one of the elder (chronologically) umps lurking.

At the higher levels, I have actually had coaches purposely try or had to do illegal moves with their lineup. I have had them tell me that they know what they are doing is illegal but they are doing it anyway. Keep your mouth shut. It is the job of the other coach to catch them. You can not tell them they may not do it. If they do not do this, they may have to forfeit.
I would just ask them rather strongly: "Are you sure you want to do this coach?" Then go about my business.

I guess it may be dependent at what level you are talking though.
I am all for preventive umpiring but you can only intercede so much.
You can not coach for them.

If you can sort of steer away from a cluster, it would probably be wise but sometimes you have to keep your place.
Remember the old saying in ball is: :"It ain't cheating if you don't get caught."

I guess this is a "sticky wicket."