Problems are still ongoing... my attempts to deal with the corn haven't made a difference and it's nowhere near being hullable as it's concave. Long story short, I suspect J has a corn
and a worn pad (the worn one being the one that was cracked, behind the pad with the corn).
Treatment for corn: soften it, walk on soft ground and avoid hard ground, maybe wear a boot.
Treatment for worn pad: toughen it up, walk on smooth hard surfaces, don't let it get wet, don't use a boot as it will prevent it from toughening up. Soak it in salt water (J wouldn't let me do this for long enough), but don't take him to the beach as sand is so abrasive.
So pretty much mutually exclusive!
His slight limp on hard surfaces got worse 2-3 weeks ago and he also showed signs of general stiffness, like being very creaky after he'd been lying down for a bit, so I took him to the vet. We suspected that as well as the corn & worn pad, there was a bit of a joint/muscle issue going on too. So he's had a short dose of Rimadyl, which has made a difference - he's now back to where he was before he got worse, suggesting the Rimadyl helped with the joint/muscle but not with the worn pad/corn. The vet wants to see how he goes now the Rimadyl course is finished - he thinks J is old enough for joint issues to be expected, but nothing like old enough to warrant being on Rimadyl the whole time. (I may experiment with Boswellia if I think he'd benefit from long-term anti-inflammatories.
I'm now thinking I need to address the worn pad, and not worry about the corn for a bit. I've looked for creams etc. online but the only ones that seem to be specifically for toughening pads are only available in the US, and I'm wary of using something like udder cream or Musher's Secret as I don't want to soften it. I'm not sure whether 'keeping the pad dry' means no walks on grass or mud, and no walks on wet pavements, all of which could be challenging in the autumn winter, or whether I just have to dry them well in the house (though surely they'd dry on the carpet anyway?). And almost all of the heathland round here is very sandy, so that would be hard to avoid.
Plus, though walking on pavements may well harden up his pad, there must be a point at which it wears it even more... So how best to balance all these requirements?
We had a 1 hour 40 mins mostly pavement walk this morning (he chose the route, I got a bit lost in a housing estate I'd never been in before

) and though there was a slight limp most of the time, it was no worse at the end than the beginning (if anything, a bit better) and he was still happy to keep going and not showing any signs of discomfort other than the limp.
Sorry for the long post, but I wanted to get all the detail in!