Best way to renew parent's B1/2 visa is to go to Canada or Mexic

Best way to renew parent's B1/2 visa is to go to Canada or Mexico, then come back. Now the B1/2 visa is one-year and multiple entry.

Here are steps:
1) After 1st 6 month stay, go to Canada or Mexico to get another 6 month stay 2) After 2nd 6 month stay, go to Canada or Mexico again to get 6 more month stay before visa expires
3) Before the 3rd 6 month stay expires, Use I-539 to apply for extension

Therefore, ideally, your parents can stay for almost two years.