I build fences occasionally.
The way I lay out a two thousand foot line with obstacles in the way is with spotter posts.
I use two and three eighths inch light wall pipe because they're light enough to tote and with their thin walls easier to stab into the ground. On a long line like you're describing I will use some marking paint to color the post a contrasting color against the background. It it's blue sky then I'll use a flourescent orange or red, treeline or something dark I'll go with a white.
I go to each end and measure in from the survey pin a set distance. Shorter is easier to work with so if I can get away with three feet I'll use if over five or six feet. I stab in a marking post, seven footers work great, sixes are okay, eight footers if there's grade variances that cause a problem. I plumb up the posts (make them straight up and down with a level).
Then I go to the middle with a helper and another marking post. I have the helper move the post in or out plumb, plumb is important, again straight up and down. I then go to one end or the other and look down from one end post to the other. I move the helper in or out as required until the three posts are in a straight line. We stab that post into the ground and plumb it up. After checking it again for being in line we move to break up the distance again by the obstructions. We put in more marking posts in our line inside the property line on each side of the obstruction.
When we have all those in place we can then place new marking posts along the property line by measuring over exactly the same distance from our inside posts. I go for two inches inside the property line. It gives the property owner ownership of the fence even though the neighbor gets the benefit of it. The neighbor can't grow stuff on it or paint it because it isn't theirs. If the fence cost is being shared by both homeowners then the fence is placed on the property line.
Keep in mind different states have different rules. I've fenced in Arizona, California, Oklahoma, and Texas. The above works in those states. But I know that some states have different rules for their fence statues.
Once I have marker posts then I lay out my post spacing. Back in the day we used claw hammers. I still have a twenty eight ounce Eastwing with really rounded ears from marking post spacing. Now I use marking paint because I have it with me anyways because the locating companies want paint marks where the fence is going to go. Which brings up a very important point. BE SURE AND GET YOUR LOCATES!!! Some things are obvious like the telephone or gas lines should be in the right of way. Here in Texas the water lines can be anywhere, path of least resistance and day of the week matters when it comes to the water lines. Day of the week because some days the operator is more alert or less hung over than others when it came to operating the trencher.
With the spacing laid out, I use eight foot centers because I do a lot of pipe fencing and I get it in twenty four or thirty two foot lengths. With the spacing laid out I lay out the line. Again I use the sight or marker posts.
For the rookie or do it yourselfer I recommend the plumb man method. That's where you stand behind the end post and look down at the next marker post. The helper takes another marking post and puts it over the spacing mark and hold it plumb. You move him in or out and until it lines up with the next marking post. When he has it plumb and in line you have him mark the spot with your marking paint. The helper moves to the next post and you do it all over again.
I can do it with or without a helper. That's because I back sight. I hold my marking post and look down at the next two marking posts. When I have the marking post in my hand plumb and in line I mark it and move to the next one. I only use string on short lines when it would take longer to set up marking posts then it would to drive in some stakes and pull a string. Western fence men don't use strings. In fact a lot of fence companys will not even consider hiring a man who is used to using string. Everything is expected to be done by eye. (Texas for the most part isn't part of the west in that statement).
When people ask me about the string thing I point out that people who use a string invariably check their work by eye. We skip the string part and go straight to the eye from the get go. Another thing is the string will sag or sway in the wind no matter how tight you pull it. The eye has none of those problems.
After the posts are laid out with X's or crosses over each post hole then we do the posts. Once again it's all done by eye, height and line at the same time.
I hope this helps.
