Fence flat roof boundary?

[WouldntItBeNice2]

I have very nosy neighbours who think everything they see is theirs. We share a wall and have flat roofed extentions at the back which are joined but the roofs are slightly different heights.
Their window onto the flat roof opens all the way, and recently they brought a visitor across the roof to our bedroom window. After a few moments one of them jumped or stamped and then both sets of feet ran back to their side.
When I went out they were standing toes to the join, making big sweeping gestures over our garden as if showing them around.
They have form for this type of behaviour, especially at the front window, but actually taking someone to our bedroom window was a new level. Sometimes I sit in bed naked reading, or, you know, do things with my husband.
Anyway, I have googled a lot, and know there are restrictions for fencing the edges of a flat roof, but can I put something up along the join?

I am in the UK.

Paint it with something very sticky.

Anti climb paint but make sure you put a notice up stating it’s there. Obviously that only need be on your extension wall and therefore not visible from the actual flat roof.

If it's a felt flat roof be very careful about fixing anything into it. In fact, no one should even be walking on it unless absolutely necessary as it could cause damage.

We had a similar issue in a previous house 20 odd years ago where the neighbour's workmen caused £10,000 worth of damage by walking on our roof, putting heavy items onto it, and fixing items into it with nails, all without our knowledge or permission. Water got in and caused a great deal of damage. We did get compensation eventually but it took a year and a lot of stress.

I think you need to make it quite clear that your flat roof is your property and that they are not to come on to it without your consent. If it's a felt roof, this Is especially important.
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We did make it very clear when they were refelting theirs maybe a decade ago and their workmen were walking all over ours. They argued that it was meant to be walked on and carried on. Our felt held up ok, but when we did replace it the board under it was smashed up and soaked.
Sadly making things clear makes no difference to them.
They are not coming up a wall to it, just walking across from their own adjoined roof.

I have a climbing plant (the sort that doesn't damage what it climbs on) and thought I might tie some wires or a rope ladder or similar between it's pergola and a hook already in the wall. Honestly unless they are physically prevented they will continue.

The plant idea sounds worth a go. Good luck!