If you want to make your outside fence five or six feet tall, then it can get expensive. That being said, a relatively inexpensive option to consider is going with 60"h x 100' 2x4 welded wire ($90 per roll at TSC) with t-posts, and then overlay the bottom inside of the perimeter with 24"h 1/2 hardware cloth, mostly to keep the chickens from sticking their necks out through the 2x4 fence openings. You would need to tie-wrap or wire the hardware cloth to the welded wire fencing. You're still going to have a potential issue with snakes and hawks; but dogs, raccoons, and foxes will be kept out. You could also add some inexpensive plastic bird netting if you want to keep most of the snakes out, and you could top the run with 2x4 welded wire to keep the hawks away. The 6 1/2' t-posts would be about $4 each at TSC, and you would need 16 of those for a 12' x 36' run and just one 100' roll of welded wire. If you put on a top with welded wire, you would need more t-posts to keep the top from sagging and an extra 100' roll of welded wire.
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