I can see a couple, three options here....you only have 5 hens, so a small chicken tractor would allow fresh foraging without the escape issue. One can be made quite easily out of cattle panelling, chicken wire, 2X4s, fencing staples and zip ties.
OR....you could purchase some fiberglass electric fence posts...very slim and lightweight...and come inside your perimeter fencing about a foot or two and erect a fence out of plastic deer or poultry netting. Easy to erect, easy to take down when you leave, virtually invisible from the outside of your fencing and easy to store when you no longer need it. They shouldn't fly over this and onto your perimeter fencing.
OR...use electric poultry netting and the fiberglass posts and erect a large free range within your perimeter fencing and just move it on occasion to a new area of the yard....say, section your yard into 4ths or 3rds and just rotate your free range.