I sectioned a field in two with electric and thought it worked fine, then started noticing loose bits and a couple of the lambs were getting between the strands. I had 3 strands on a 3ft plastic post. I wasn't that bothered as there wasn't anywhere for them to go and they seemed to of got back ok but after a week one of the other sheep must of copied and pulled the posts across the field snapping the wire. I still use one strand of electic on a 3ft post to keep the horses off some parts of the field, she sheep just duck under it.
I imagine it'll be very expensive to stock fence it off.. 3 acres is probably around 450 metres, at £5 a metre, thats £2250! I'd want a seriously long lease before investing that in someone elses field!