Joinour the neighbours warned us to shut the gate when we moved in, on the poo basis. It's a known issue and shutting the gate worked for the others - and cats wouldn't stop pooing at weekends, really, either, or work to a schedule of that kind. I think it's as simple as the dog getting used to our garden while the house was empty, and the owner (who is, by definition, a lazy fucker) doesn't want to wait for them to crap. If they're very used to our garden as the poo space then Pavlovian response has probably kicked in.
Thanks so much for the padlock-from-6.30-until-8.30 suggestion, and the Jeyes fluid - that is also a genius tip; DH is now home so will pop to Homebase and buy some, and treat accordingly. Think those will be the way forward for now, with motion sensors to alert us if all else fails/they get up earlier.
Kids can't deal with my handling this first thing. Eldest is autistic and suffers severe anxiety - he could get massively hung up on this situation if we let him.
I'm probably paranoid after working for a neighbourhood mediation charity a few years ago, but I would be very wary about escalating this. Someone capable of it is not going to have good boundaries or much concern for other people'. Poking that stick is less sensible as first recourse than trying to deter the dog to begin with.
But if we do need to confront we will be recording the conversation on my phone. So will update accordingly. I'm very much hoping it never needs to come to that, though. I just doubt this person is going to be especially reasonable, and as this is a civil and not a criminal matter, formal avenues to stop it would be expensive and not necessarily that effective. Think we will have better luck if we can deter the dog.