This is a weird scenario.
My neighbour lets their dog pee on their side of our shared fence. (They deny it).The dog pees on their side, the urine flows under the fence and into my side. Photo below shows a very mild day. You can see the discolouration from more substantial pees. The odor is undeniably dog urine.
QUESTION: I was wondering if I could somehow seal the bottom of the fence on my side so that the dog pee remains on their side. What's a cheap thing I can use?
It seems to mostly happen at the spot where the concrete has eroded. (Maybe it has eroded because it's been happening for years before I moved in to this place).

Below is the spot where the dog urine comes into my side:


The bottom of the fence seems to sit a little lower than the concrete so if the dog pees on some other part that's not eroded, the pee might just remain within the trench. However, if pee gets through the trench, it will flow towards my house as the concrete slopes toward my house. So I might also want to seal these sections.


Thanks for any tips!