*Stretches and dusts off the cobwebs*
I remember back in the day, you yung'uns won't recall... When OFP was fresh and smooth like a new born babies bum... In Wolfs Mission Masterclass, *Laughs*, I did a section on this very subject.
What I stated, was that yes, when people play your mission, they will try and cheat their way through it. Why? Various reasons. To see if they can beat the mission, beat the author, find new and inventive ways of dealing with the problems you set them.
The one solution I could find to this problem, was to play test your mission, as the author states in his opening post, arcade style. Play it through properly, attempting to complete it in the way you intended for it to be completed. If that went without issues, then look around and try to complete it by using workarounds, or by using the time speed to alternate how the enemy reacts to your movements. If possible use the scenery and surrounding items to assist you in basically, breaking the mission.
Everytime you find a workaround, jot it down on a notepad, and at the end of the session, summarise, then ammend. For every workaround, figure out a solution.
Someone manages to sneak in and get that chopper from the compound before your realistic pilot blokey manages to get to it?
Question: Does having that chopper ruin the fundamentals of the mission?
Yes - Lock the chopper
No - Leave as is
By increasing passage of time, they can run all the way around your carefully constructed and laid out defence to find a gap that you never expected to be used, and achieve the objective or wreak havoc.
Question: Does that factor ruin the challenge and does it skip important waypoints?
Yes - Place extra units, or create impossible to pass barriers.
No - Leave as is
Gamers are ingenious little creatures, like the pixies that sneak into HuBBas house at night and pleasure him whilst he sleeps. He know's it's happening, he just doesn't know how to stop it.
You need to do it yourself, and see where the flaws appear.
You'll never make it foolproof, but you'll certainly give the sods a run for their money, and if they persist after that point, then nothing except rear end loving from a donkey will make them happy.