I just did a “temporary” (temporary enough to easily take down but will likely be permanent) dry lot using Horse Guard fencing. I set it inside of the fence line by 2-4’ depending. The property fence line is barbed wire but I didn’t want to mess with getting the horses close to that so I set it back enough that they can’t get into it but not enough that there’s a wide gap. That side of the property is a lot of lava rock and scrub brush so it isn’t useful property anyway - I wouldn’t ride there and nothing but sage brush is going to grow there anyway so I don’t really think it matters. I do have a “boundary” on the other side which is a road/path (on my property) that I use for trails or to access the back side of the property so I was limited by that line and wanted to get as much space as I could.
[QUOTE=ReSomething;8181814]
If we ever go to the back and put up fence there, where there is truly crappy field fence and barb wire and no longer any livestock, my intent is to go right to the line with my fence even if it pushes up against theirs and possibly rip out the old fence. We have got good pins for our corners but I don’t want to get into the “that two feet must be mine now” argument. …?[/QUOTE]
This. If anything on the other side add a hot wire on top that discourages livestock interaction.
2 foot means lots of things can grow up and you won’t be able to control foliage growth (trees, bushes, poisonous weeds, etc.). 12 foot may mean you can mow but is a LOT of room to loose (especially if you have a small piece of property.
Plus some states have laws where if someone starts “using” the property outside of their fence - it becomes the property of the “user” - they could build things like a shed, etc…
Just build your fence as close to the property line as possible with a hot wire on top to prevent any interactions with their livestock. If their livestock is questionable (bite, kick, not inoculated, etc… ALSO put a hot wire inside your fence to keep your horses from reaching anything which may come up to/over the fence.
[QUOTE=Pocket Pony;8183121]
I just did a “temporary” (temporary enough to easily take down but will likely be permanent) dry lot using Horse Guard fencing. I set it inside of the fence line by 2-4’ depending. The property fence line is barbed wire but I didn’t want to mess with getting the horses close to that so I set it back enough that they can’t get into it but not enough that there’s a wide gap. That side of the property is a lot of lava rock and scrub brush so it isn’t useful property anyway - I wouldn’t ride there and nothing but sage brush is going to grow there anyway so I don’t really think it matters. I do have a “boundary” on the other side which is a road/path (on my property) that I use for trails or to access the back side of the property so I was limited by that line and wanted to get as much space as I could.[/QUOTE]
The thing about a 2’ gap with something like Horseguard is that you can still turn the fence off and get a weedeater under it and trim, or you could spray I suppose. With no-climb, it will be quite effective at keeping humans out of there to bother the plants. 
Why not put the permanent fence right on the line, then adding an electric fence 8 feet in or whatever if you have neighbor problems.
Thanks everyone who’s chimed in. Lots of food for thought. It’s a small space so I’m reluctant to give up much space. Don’t want to spray, but would only have to get around sides 1 and 2 to push mow the gap. Good point about needing to brace side 4 for centaur, this would be a straight ton. Wanted centaur for bouncability.
I will let you all know what we come up with. Terribly excited as we make this into a horse property. Scouring the small barn design threads too.
*straight run
Something to know that took me years to figure out is that it’s not just an accident or mysterious chaos that causes weeds to grow higher and more thoroughly directly under the fence line - dew collects on the fence and drips down to make that extra nice habitat, plus the fence protects the plants from being trampled etc. Birds sit on it and poop out the most annoying possible seeds, too.
On the side with the road…there may be legal setbacks for “right of way” that are more substantial than required for a regular property line. That type of setback is measured from the legal center of the road. Be sure you understand the legal requirements before you install your fence.
For the record…I agree with the others that you need a buffer between your fence and your neighbors for both maintenance and other reasons.
We are supposed to have 30’ between horse pens and property line, so we have a track around the horse pens for walking with the dogs. Our neighbors don’t heed deed restrictions and let our fence keep their horses in. Nice… I agree about leaving space between fences just for the safety/wellbeing of your horses.
On one side of our property neighbors put very sturdy railroad ties in the ground. Over the property line and slightly onto our property. We attached our fence to it on that end, since it is on our property.
The sides where you will be boardering privacy fence you may need more than 2 feet. I have about a 3 foot gap between my noclimb and a neighbor with a privacy fence. My horses chewed up the top of their fence pretty bad. The neighbor never said anything about it, but if he did I would have been responsible to replace a whole lot of his fencing!! It got knocked down in a hurricane, and had to be replaced anyway. I have put up hot wire on my fence and that has worked to keep them away from from the neighbors new fence!! It’s been 10 years now and no chewed up neighbors fence!
Be sure you check with your local town on possible mandatory set-backs if you are staying close to the property line. I also wouldn’t be taking down fence without notice if it was put up by neighbor
