My neighbours dog sometimes strays from his back garden into mine. Our
border is hard to secure as there are many rhododendrons etc., and
it's not normally an issue. We get on very well

The issues are that perhaps his dog will get out via my back then
front garden as I have no gate

Also it's leaving some unwelcome mementos behind.

I'd hate to upset my neighbour, it's his boundary .

I wondered if there are humane deterrents that will keep dogs out ?