How to prevent double calls

[umpduck11]

1) I don't make an out call on an obstructed runner, therefore there's no need to reverse the call. Why would you call an out if you know the runner's
been obstructed ?

2) Knowing which bases are which umpire's responsibility will keep this from
happening every time. It's something I go over in pre-game. No need for any
"secret" signs either. If the player appeals to my partner and it's my call, I
will call out "Bill, I've got this", that way the teams knows it's my call, not my partners.