Is there a recommended number of treatments to avoid Botox resistance?

I am currently looking into getting Botox for my jaw and forehead. While forehead and frown lines can be covered with fillers or other procedures, I am particularly curious about resistance since Botox for jaw muscle reduction seems to require periodic injections. As Botox has become so popular, there are many positive reviews, but it seems there are just as many questions and reviews regarding resistance. Based on my research, I understand that if resistance develops, no matter how many injections are given, it will be ineffective and there is no solution. Does developing resistance vary from person to person? Or are there recommended frequency or treatment cycles to follow to avoid resistance? It seems that as long as there is no resistance, Botox is the most effective treatment for jaw muscles. I would appreciate candid reviews and information. Also, for those who have seen results with square jaw Botox, please let me know how long the effects lasted.