Problem solving a fence in a tight spot. (Bonus shitty diagram)

I've been wanting to block off the narrow alley next to my house with a privacy fence. Ideally, the entire fence would basically be a gate as I would like to have the option of parking a trailer or RV there one day. My problem is that all of my utility lines enter the property through this 11'9" corridor.

As you can see in this completely to scale drawing the gas line is only 20" from the garage and the power line is only 20" from the neighbor's fence, followed by phone and cable. Somewhere in there is the water line.

My original hope was to place posts right up against the garage and neighbor fence and have a double gate in between, but I used to work in underground utility construction and recall that you are supposed to give 18" on either side of the locate paint, which leaves me with no room. Even if I did carefully dig up and spot the utility lines, putting concrete anchored post right next to them seems dangerous should the post ever get knocked over or need to be replaced. Anyone see something I'm not here?