a great way to beat hecklers in a card routine which requires control is to control their card so it is the 2nd one down.
Then when they say its on the top say "no its not, take it and look yourself", then take that card and place it in the middle. And for fooling purposes do a DL and say "see, it still isn't on the top."
After that they'll shut up and let you get on with the trick.
But to be perfectly honest i usually just classic force their card onto them so if anything does go rong (like they put the card in the rong place ect.)
you know exactly what their card is.
And to find it again, just spread thru the deck face up and say "see, your card is completely lost in the pack", get a break under their card, cut the pack, throm in a couple of false shuffles, then continue
hpe this help
Joe - The Magical MoJo