Ok, here's photos of our driveway.
You can see the orange wall at the entrance of our driveway. There's great forage to be had on both sides of the driveway.
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This next photo shows this forage up closer. Unfortunately I don't think there's enough room here to put an electric fence down this side of the driveway??
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I think I see the origin of the problem. Looks like a powerline runs down the side of that roadway as well, and anywhere I have ever lived in the world, an easement is granted to the power company, whether private or govt owned. One of the stipulations in those official easements is that nothing can be built on that easement that might impede the power companys' vehicles and equipment, or that the powerline might fall on should there be a wind storm . This is probably where your neighbor is getting the "you can't put anything up along the road" thing.
I have a similar deeded easement all along the west side of my property--it too began as a powerline easement decades ago. 35' wide easement, and I cannot put a fence up closer than 17.5' either side of centerline of the easement. I am allowed tho, to put gates across it, as long as I leave them unlocked or allow the power company to put one of their own locks in the chain behind my own lock, if for nothing else than to allow the meter reader full access.
You may not need an attorney to sort this out.
You will need to go down to whatever Thai entity serves the equivalent of local county clerk office in Thailand and find out what deed restrictions actually apply.
Easements, even in the USA are a funny thing. Pictured below, is the survey plat for 17.3ac I purchased (top left) as well as a separate parcel I own (41.4ac bottom).The easement is denoted by a broken line with the letter 'E". The roughly square shaped solid blue line is the propertyline for that 17.4 ac. Note that it includes the easement and that at the top (North) side, the property line extends out into nearly the middle of a paved state highway; FM 945. That easement was granted many decades ago when the state took over what was then not much more than a pig trail of a dirt road.
There is another 41.4 acres (not included in this plat) just to the south of me belong to one of my sisters--it too has a powerline easement along it's west side and serves as my primary entrance/exit road.
The above plat was created during a survey made when I sold that 17.4 acres to someone outside my family. The title company called me a week before closing, and said closing would be delayed because none of the 3 current titles met Texas statutes in regards to egress and digress. It is no longer eagl to sell a piece of property if it would landlock another piece of property--an egress/digress easement MUST be granted and spelled out in the deeds. This of course, was to my advantage, since I was "the one n the middle". At closing the new owner and I discussed the easement with the title company rep. She explained that the easement was solely between the parties involved and no one else. Myself, my sister, the new owner and the power company and it's representatives. None of us landowners can legally authorize anyone else to travel over the portions of the easement that is on another's property--not my friends, new owner's friends, not relatives or anyone else. It's just binding between the 4 parties involved. The easement property itself is still ours of course--we pay taxes on it and maintain it--yes, the new owner, just as I did, is paying property taxes on the portion of that 17.4 acres that lies under and along state road FM 945..
You may find, that there really isn't any kind of relative law at all in Thailand--it may just be a cultural tradition, which would probably be more difficult than a real law, but if you do find that you can legally place a gate across the road, I would suggest a solar powered electric gate and just give the other guy the keypad code.