The old expression: oral contracts are not worth the paper they are written on. Get it in writing before doing anything.
^^
I agree. This isn’t an agreement between two trusted friends. This is a business kind of thing. Get it in writing. If you feel uncomfortable with going “that far”, you can at least do it by text or email. State what you spoke about, and ask him to respond.
“I am writing to confirm the substance of the conversation we had on xx/xx/xx concerning the fence at xxxx. Detail here. If this is not your understanding of our conversation as well, please notify me by mail within ten days.” DH has written many of these kids if letters to memorialize a conversation. Works pretty well!
Dies the developer know about the school access, I wonder?