I use a small hand-held recorder (about £20.00 - new), for all the Speedwatch stuff we do to record speeding idiots in the village.
Yup, it is a small financial gulp, but so easy to use, replay and record from, I wouldn't be without it! The replay is a doddle, and the files are so easy to listen to; typing is very easy with a pair of earphones like you use for all that opera you keep listening to!
Ebay do loads of them!
I wish I'd thought of recording our locals like you're planning. They're all gone now...