FARM FENCING?! how far apart should my posts be, and what size post?

Okay, I have a smalllllll horse farm, almost 9 acres, and I need to put up new fencing. I was looking at getting 4 inch by 8 ft posts (we're on the morraine so they ain't coming out!), and looking to space them 10 feet apart, is this okay? or should I do the 5 inch posts, and 10 feet apart, or just stick with the 4 inch posts and 8 feet apart. I'm planning on putting 3 boards up, and two lines of electric poly rope off the boards (at shoulder height, and at knee height) to keep the horses from touching the fencing, which is something I KNOW works well.

HELPPPP PLEASE, THIS IS URGENT, i need to place my post order SOOON, i move in like 3 weeks!

We're not using the farm wire fencing, like the paigewire, it's already "up," but literally most of it is on the ground aha. We were going to take out the posts in the first two fields (currently one huge field, to be seperated into two, because on one side we border our neighbour, a farmer and we're waiting to see if he'll extend his fencing from up by our drive-shed, all the way down to the end of the property when he sees we have horses), we were GOING TO/thinking of just putting in 5 inche posts, every 10 feet  and 6 inch on the corners, and at the gates. Then, we'd run three wood rails, there's a cedar supplier by the farm that sells for half the price of the co-op stores, and infact sells to them too , and then we have the screw in insulators for our white poly rope which will be at all the posts, and we're going to run a line of the electric fencing around the inside at the top, and eventually depending on how much extra fencing we have, we'll run a second one at about knee height. I don't know where you are, but that centaur crap is.... well crap here, and REALLY FREAKING EXPENSIVE, as in you could easily spend half a million on your farm in it, and well... we're not even close to rich aha. We know how to run our electric, and since we've been horse people for well over 10 years, we know and already do introduce our horses to the electric wire the minute they get in the field, so they KNOW it's there, and won't go near it. We have a 10 mile solar fencer, we only have 8 or so acres, so it'll be fine and yes it's on 24/7, but it's low impedance so it's not going to like... blow up on us . We were going to check out one of the stables around our old house and measure, but at the moment I'm thinking 10ft isn't TOO bad, but if it comes down to it, I'll do the 8ft. It's not like our property is gigantic, the front fenceline is 317ft long, and up to the end of the paddock is 310ft, depending on whether or not we crop out all the moraine rocks that are currently on the fenceline, and move the fence back like 4 feet on each side.

Oh and, I forgot...ours I THINK might be 20ft apart, the wood posts, with a tpost in the middle, and most of it is standing near the top of the "hill," or knoll by the drive-shed, it's down by the road that it's taken a beating, but I think that's because down by the road theres some of the morraine sticking out, and they've put the posts between the rocks, which clearly hasn't worked out!. We're getting rid of all the crappy farm paige wire, and barbed wire, and old electric cattle wire thats "chillin," on the posts, pulling the posts out, and putting new ones in about 4 feet in from the old fence to get away from the morraine poking out. I think 5" might be okay, and at the moment 10ft is looking alright too, but I'm going to go and take a look at a friend of ours' farm east of here later on, and measure hers, since hers is rather nice and sturdy.

Yeah, we can't use the 10ft posts, we're on the canadian shield, so we have to use the 8ft and set them like 2ft in, but we've decided to cement the perimeter posts in place, almost like you cement in residential fencing we're not sure yet, but i think i'm going to go and measure the fencing at a place we used to board at, this guys fences have been up for like... 60 years, just your regular 3 board, post system, and if they're 10ft apart, then i'll go with 10ft.

It makes sense, we have a 317' frontage onto our street, we were thinking of only concreting those posts that line a road/driveway, so we have something around 60 posts to concrete, which doesn't even end up being THAT much money, of course free being cheaper in the means of "jogging," your posts. So far we have to buy something like 126 posts, since most of the posts on the property were poorly taken care of, and have since... let's say "died," and fallen over. At one point, the farm fencing, the wire mesh, has actually grown into two elm trees, making a lovely high tensile fence, seriously! it's perfect, except that it's in two trees, and farm mesh fencing haha.

We've decided to go and measure a fence at our old boarding place, just to make sure we can do the 10' spacing, but as I say... we've never once had an issue with horses going to the fences, infact we like to discourage them from going to them at all. We've always introduced our electric fencing to our horses, so they know its there, and won't go near it. It makes life loads easier, and plus lets keep in mind we're only having 5 horses on the property 5 who will be out 24/7 for the first year or so, and then possibly in stalls at night, because we have yet to renovate our bank barn so the stalls are well... enclosed properly and not falling apart. The previous owner obviously roughed it.  However, I have been to, and seen fencing for horses that's been practically on the ground, with a bit of electric wire around it, and the horses couldn't give a crap about it, they just don't want anything to do with it. I guess there is much of a difference between farmer standards, and horse people standards because the riding school on our street, that's about 20 farms away has the crappest looking, falling down fencing, with a bit of electric tape around it, I have ever seen, yet the rest of the place is pristine, and the horses are never near the fence.

Plus, it helps we're there almost all hours of the day, a break-out is pretty unlikely to happen when nearly all the windows in your house have a view of the paddocks I suppose horses are like chickens, if they get bored, SOMETHING IS GOING TO HAPPEN.