When setting up multiple triggered campaigns, how can I be sure a mailer wont hit the same address twice?

Under the Suppressions tab within your Account Settings, you will see a place to enter a number for Minimum Days Between Mailings. 

This acts as a frequency cap to prevent mailings from hitting the same address too often. When sending yourself multiple samples, remember to change this setting to 0 or else a number of them will be suppressed.