trimming flight feathers is your best option for grounding him...electric bird fencing could be another option...bird netting does come in huge rolls/bundles, my last order covered a 50' by 500' area so your small area is easily covered
The problem with clipping just one wing is if they roost on anything they lose the ability of gliding down to the ground and may land on their side or even their back possibly injuring themselves. I clip both wings flight feathers leaving two or three tip feathers to protect the wing bone. If you get a strong flyer take more feathers. Also, be sure they're flying out, many of my birds can hop 3-4 feet onto something.
This guy is flying, not hopping. I watch him do it. He can fly 6-7 ft up to the top of the fence, then down, or he flies from the 6' tall gate up to the top of the coop, then down on the outside of the pen. We haven't cut anything yet. I am still debating. I absolutely loathe the look of clipped wings, but I also hate for him to just be out alone and more vulnerable than everyone who is still inside the pen. I just have too much on my plate right now with Isaac to even deal with him. They're all inside anyway due to the temperature and windchill.
Sometimes you'll get a strong flyer, no doubts, but more often than naught they'll stay grounded. My guineas are my best flyers and I don't have issue when their wings are clipped. Not barring the exceptional. Oh, keeping the tip feathers also give the illusion of a fully feathered wing when they are folded up.