I haven’t attempted the double harness, but general advice I got when asking around for avoiding escapes was that where there’s a will, there’s a way for cats. I think the ultimate answer is to make sure you train them to see you or a carrier you always have nearby as a safe retreat. We didn’t train that young enough so we only go on walks right in front of our home and when she does get spooked enough to escape, she at least knows to run back to our door.
I haven’t attempted the double harness, but general advice I got when asking around for avoiding escapes was that where there’s a will, there’s a way for cats. I think the ultimate answer is to make sure you train them to see you or a carrier you always have nearby as a safe retreat. We didn’t train that young enough so we only go on walks right in front of our home and when she does get spooked enough to escape, she at least knows to run back to our door.