It’s not that ticks can’t attach with Advantix, it’s just that it contains a repellent so they are much less likely to. If they do, they die. The thing with ticks is that for most of the nasty diseases, the ticks need to be attached for more than 24 hours for the disease to be a higher risk of being transferred, so as long as you’re thorough at checking your dogs after every walk, it doesn’t “matter” if they have attached in the meantime. But I don’t want them in my house, on my furniture and in my bed!
In practical terms, with my dogs, I have found every tick while it’s still “empty” except one on Luna’s leg. Because of how dense her coat is, it’s simply not possible to check her for ticks.