I am having the same issue too. My horse is double bellbooted ( velcro bell boots over pull-ons). Hoof supplements and other treatments that go directly on the hoof to make them stronger work great too. Talk to your trainer, farrier, vet, etc.
Unfortunately I don't think there is any other method but if you are looking for bell boots that will actually stay on I recommend pull ons over Velcro
I just already use them and I wasn't sure if something else could possibly help @gracegarey
Why are you opposed to bell boots?