If you don't want the letter carrier bothering your dogs just put a box on the street. Or, rent a post office box and go get it yourself every day.
However, when you place a mail box on your house you have INVITED the letter carrier to go up your path to the box.
Frankly, I think that's an antiquated way for delivering mail and should be eliminated, but legally speaking, the burden of any injury to the carrier is yours and the Postal Service will sue you for loss of his services while he recovers.
My house was built years before I moved in. I have nothing to do with the local mail delivery protocol. I now keep the dogs in until the the mail is delivered. It was only after the last regular mail guy retired that we had ANY problem. The issue is with the USPS giving door delivery routes to dogophobes.