Over the past couple of years I have been using small plastic electrical ties to secure the zipper and locks on my checked bags. After inserting the end of the strip into the locking end of the tie, it can not be reversed and has to be cut off. However, they are relatively cheap so that doens't matter. After locking the zipper sections it can be opened up slightly, well enough to insert a small nail clipper which I use to trim off the ties so no body can try and pull on them.
I have only had one occasion early this year on my return from LAX when after collecting my bag from the carousel, I noticed one of the plastic ties (one section only) was missing. If anyone has seen these ties you will appreciate that they are quite sturdy and I don't think they could be broken off, so before looking into the bag I approached a customs officer, explained the situation. He then inspected the section in question, inspected the section, and they he passed me through. He did not want to inspect the other sections because the ties were intact. It might be a cheap alternative for some pax, and a small bag of them does not take up too much room in your bag.