Hi Harry, I'm sure Pamda will be along soon I'm sure, but thought I'd put in my 2 cents.
Cable ties can be picked up at any hardware type store. Home Depot and Lowe's also carry them, if you have those in your area. Be sure to take extras along in case you have to open your luggage for inspection. Need to hide some nail clippers or something in a luggage pocket that is not secured, so you can have something readily available to clip the ties. I use to carry something to clip the ties in my carry-on tote, but now that may or may not make it through security.
Cable ties are great I think. Of course they will not keep someone out of your stuff if they really want to take a look, but at least you'll know if it happened. I think it helps, as they say, "keep an honest person honest".
Another Idea for Gail along with the cable tie's...tell her to use some sort of character Identifiable luggage tag for her suitcases since they all look alike when sitting on the dock. I purchased some large neon tags at Wal*Mart so I can spot my bags a half a mile away . I saw on another post where someone used theme typed tags such as tropical fish (they were crusing down south). Anything to make it easier on her.