You can't always pick the cards, sure, but you always control where you fire... Besides, you're asking for something more complex than you seem to realize (though you're far from alone here in that regard :P). The shields are there to stop you from using your turn moving into or staying in a deadly spot. Checking to see if the spot you're in is safe but one you could make deadly is (besides clearly being a misplay on the part of the player) not so simple to program, especially now that there's a card that can fire a pellet outside even your selected firing arc. That's a lot of math slowing things down just to try dealing with a player skill issue; as it is, the shields aren't perfect, sometimes blocking 100% safe shots and NOT blocking 0% safe ones in rare cases, and that'd be tough to figure out without even going down the "discovered mate" route. So maybe avoid taking the card with "blunder" right there in the name until you can keep from doing so, and maybe always take Black Mist when you have the chance (which WILL save you from "discovered mate")? Good luck to any mod makers that try to "remedy" discovered mates - sure, it probably CAN be done, but it'll be a LOT of work... work better spent, in my opinion, learning the game and not getting themselves killed.
Viewing post in Shotgun King: The Final Checkmate comments
Wouldn't the programming of the shield protecting you from an opened checkmate just be similar to the programming of the opened checkmate itself? I think it's something that is being overestimated in its difficulty to create. Helps people get into the game too with more intuitiveness on an inaccurate weapon. Could always just play without shields if you're not interested in it so I am honestly confused why you are trying to make it a big problem.