Only second hand from a friend who incubated some eggs, so this might be "embellished". Destroyed incubator, escaped and he spent a silly amount of time chasing them around a wide area. They run like the clappers, kick hard in defence. You'd need very high fences IMHO. But like I say this is second hand information.
If you're after fox protection, alapcas are supposed to work. Another friend who helps out if I get ill etc and who had some of the land I'm on before me had a couple. Have to shear them apparently, and they spit at your face in defence (and presumably kick/chase), but he felt they were effective.
Is there a public footpath across these fields?