Usually my mare is really sensitive but when I Joined-Up with her it didn't take long at all. In the Monty Roberts book I have, it says that it's not wrong to do the join-up everynow and then so your horse doesn't forget. Or, simply test them, as they test you. Horses, as you know, will test you till the day they die, and they do so with all the other horses they herd with too. Which is why it is a necessity to test them yourself.