We use the standard poultry netting you can get from Hotline or Mole Valley or wherever. I have 2 50m lengths to make 100m for the main pen. The good thing is that if you have the space you can move it around to rest ground. There are some things to keep in mind though. You will need a good powerful energiser to run this stuff. You will need to make sure it's really well earthed too. The second thing is that as soon as the grass starts to grow, it will short out the fence. It's very difficult to keep the lower strands off the deck, especially on a sloping or undulating field like I have. We have gone some way to solving this by snipping the connector to the lowest strand as recommended by Hotline. So this means regular lifting of the fence and strimming. I have an idea this year that I'm going to pt a length of 6" Damp Proof Course under the fence to keep the grass from growing and shorting it. The problem with this is that the grass at the edges tends to push up and turn the DPC into a channel which holds water. But I think I can solve this by taking up a bucket of stones every now and again and weighing the edges down. In time, the grass should die off. I have also considered trying to pick up old slabs or floor tiles wherever I can to put under the net. This all makes it less portable of course.
I would also recommend a proper post at each corner of the net so you can strain it up and keep it tight. Guy ropes do not work all that well as the posts are bendy and tend to go out of shape over time.
I have to be honest and say that it's been a pain the whole year. You are trying to keep the grass off all summer and trying to stop the fence getting blown over all winter.
An idea I have had this year which would work out cheaper probably than electric netting is just to use standard posts every 5m or so, with those plastic temporary posts in between to make a bigger run. Then run multiple strands of metal wire around it so they are very close low down and not so close higher up. I think the chances of a fox getting through are minimal but I have yet to prove that. He won't jump it if it's on and he can't dig as they always dig close and he would get a whack. I don't think the birds would get out either. Benefits would be less maintenance and it would need less power to keep it working well. I have yet to try it.