Oh @brushingboots that must be driving you round the bend. I do hope this is the last of it. I know how much you both value those walks.
@VanGoSunflowers I wouldn't bother with a walking coat either. Bill has short, velvety soft fur (with a coarse stripe of Labrador fur down his back in the winter) and is miraculously self-cleaning - I think you need to see how mucky P gets before investing. I got a couple of noodle towels from Henry Wag which seem to dry off most of the muck, and a drying coat for when he gets proper wet (he's not very waterproof in the summer so can get a bit cold and bedraggled if the weather's rubbish - doesn't stop him jumping in every bloody pond, stream and drain in the county though). I have a back seat cover so don't mind him getting that dirty, not that I get him mucky in the car much.
On which note I think I'm close to cracking it with him in the car. So long as we're on a familiar drive, and he can rest his front half on the centre console and get the air con blowing on his belly, and lean on my arm if needed, he's absolutely fine. He only loses his mind when we start driving somewhere new, or where he knows we're going somewhere exciting. And, God love him, now he's started pressing his whole body into mine and burying his head in my arm trying to self-regulate because he knows he's struggling to cope. So I think I can try slight detours from familiar drives, and sometimes just going round in a circle to desensitise him - first bit of hope I've had on this for a while.
He did so well today at 1-1 training too (it's a very low bar, mind). We tethered him after he'd had a run round after the swallows, and he started offering all sorts of learned behaviours - sits, downs, touches - and learned new stuff like duration on the hand touch - despite there still being swoopy birds and rabbit holes and agility kit all over the place. Little superstar. Now completely conked out. I'm so very proud of him today, and very relieved - our morning walk was grim so I needed some optimism.