I would get rid of that old outmoded opener and install a new safer model with state of the art electronics.

I was hoping there was another alternative.

His receiver is probably "grabbing" your code.

Be safe, replace the old unit. if not

use an acessory lamp control to turn off the power to your gdo when you leave.

plug lamp control to outlet, and gdo to lamp control.LC controlled by newer gdo remote. Prolly costs near anew opener, but not a new opner isntalledBsafe, replace gdo!