There were no grommets involved with those particulare anklets. The design I used was largely based on the one Harry McElroy published in Desert Hawking III (and I believe II as well) where there is a tab on side and a slit on the other. As I recall, Harry described using this pattern with grommets, but if you make the jess holes just a little bigger the grommet is not needed, and it saves a potential problem point (down sides to grommets are they can cut the leather, they can work free of the leather and cut the foot, and its easier for the hawk to remove and toss the jesses because the grommet has less friction)
Makeing the anklets removeable allowed me to periodically remove them and oil them. I used to do that faithfully at least monthly, but I never really noticed it changing the service life in the leather for me. The frustration of looking for a leather treatment that would actually seem to extend the life of the leather is part of what drove me to an alternative to leather for anklets.
Also, to be fair, the incident where both anklets failed together happened during the molt when I wasnt handling the hawk much and it had been several non-rainy months since the anklets had been oiled. I did give them a quick visual check just after picking her up to bring inside for a visit. Prior to that I had anklets give out on several occaisions, but it was always one at a time, and usually when I was inspecting them for soundness.
I used leather for about 4 years after that incident, before Steve Layman and I did some head scratchin over the phone. He had done some experiments with braided anklets, and gave me some ideas to try.
One other key difference between leather and synthetic fiber materials - the synthetic materials display their wear in with frayed and broken strands. With leather, its very hard to tell between "cracked but strong and servicable" and "immenent failure". The wearing away can happen below the surface, hidden from view. Synthetic materials, at least all the ones I have tried, wear from the outside in.