I like this place for leccy fencing too as it's nice and cheap
http://www.farmcareuk.com/?section=shop&action=cat&c=1&pc=1
You need an energiser, battery, plastic posts (if your mare is anything like mine then go for the tallest ones you can afford), tape and 2 gate handles. I always got for gate handles so that you don't have to switch off your eletric to get the horse in and out.
Go for the best energiser you can afford. Mine on its own was nearly £120 and is one for cattle that does up 15 km of fencing but then my 2 fatty natives don't respect tape unless it has enough of a kick to make them think - they wouldn't even notice the pulse sent through by my neighbours energiser and battery
There are 3 clips on the energiser a red and black one that clip onto the battery and then another one to clip on the electric tape. The energiser will either come with an earthing rod or you'll need to pop your own on. Make sure this is pushed deep into the ground and that the connection are tight. I once couldn't understand why my fence wasn't working very well and changing the battery didn't help. Turned out the earth connection was loose.
I like the 22mm tape the best. The 40mm blows in the wind a lot which bent the posts. Talking of posts, I've giving up on the cheapy ones. My grond has stones just under the surface and so the spikes can get easilly bent, aslo the cheap ones become brittle in no time so when moving them about bits can snap off.
Remember to be most efficient on your battery mustn't have the tape touching anything it can earth out on so have a plastic post next to the wooden post (I tie mine to the wooden one with bailing twine making sure the leccy tape won't touch the twine). I have 2 strands running along the posts to make sure they don't try the limbo trick although the lady in the field next to mine manages with one strand the lucky thing!
Where you want your gate to be make 2 loops in the tape for the gate to hook over to keep the current going continously through the whole fence.
As for distance, I tend to have my 4ft posts spaced about 8ft apart, no more than that or the wind gets it. Rather than just running the fence through the runners on the posts I wrap it once round each post to keep it in place. Because of this I find it easier to do the bottom strand first.
The tape must run in a continuous loop but you can join the tape by tying it in a knot. No need for those fancy jointing plates
