We "lock" our luggage with those plastic zip ties! They work well, cheap, we know if someone opened our luggage and did I mention cheap?? LOL
I just pack a pair of scissors (manicure type) or toenail clippers to cut them off at the destination.
We've flown several times since 9-11 and every TSA agent or Curb Check In attendant have always said that the plastic zip ties are probably the easiest and most efficient for them if they do need to get into your bags for any reason!
Have a great time on your trip! We leave in 4 weeks from today.
Heidi