I addressed this in September with a direct, calm conversation, stating the arrangement was going to be more limited going forward. Sandra replied that she thought I was "more open to sharing." That sentence suggested a perspective in which my pool was a community resource, and my desire to control access to it was a character failing rather than a property right.
I noted the tone. I added a new lock to the gate. I considered the matter closed for the winter.
The following April, Sandra came to my door to discuss "arrangements" for the new summer. I informed her that my decision was final: I was not offering pool access that year.
She left unhappy. Then, the situation devolved into something I could no longer ignore.
It started with the fence. In late May, two boards in the shared wooden privacy fence had been loosened—pushed inward to create an eighteen-inch gap. I repaired them. In June, after a work trip, I found the pool chemistry depleted, a foreign flip-flop on the deck, and the fence boards forced open again.
I did not get angry; I got methodical. I installed four motion-activated, night-capable security cameras logging to cloud storage with timestamps.