I know this is going to sound a little weird, but hear me out. Don't lock your knees for an extended amount of time at a wedding. I have a friend who told me he fainted at a wedding recently because he locked his knees for too long while standing.
Let's face it, you're going to be standing up a lot, and probably for a long time. Some people have a tendency to lock their knees for balance and stabilization. This is bad for you because, according to Dr. Richard Nicholas from the University of Arkansas for Medical Sciences, "the low rate of blood return to the heart in these situations results in hypo-perfusion of the brain and at times the fainting spell. Standing at attention, or with one’s knees locked, may amplify the process."
So with that said, don't force the muscles in your legs to stay in one position, and be mindful of how you're standing to prevent a disaster.