
<<built up gradually to this kind of excercise but I would have thought anyone would realise that.>>
Don't assume anything, Tigge-with-spot! My vet told me of a nitwit who, to train his dog to run with his ponytrap, tied the lead to the axle and went for a five-mile trot around the roads. It took many weeks of treatment for the poor things pads to recover. The continual pounding on the tarmac had worn them away.
Tarmac is very unforgiving for feet and bones. It is very damaging to its bones to ride a horse at speed on tarmac (apart from the lack of grip), whereas it is fine on 'natural' ground. It is the same with dogs. The dog will be better on the verge, not the road.
Hiking holidays are fine, because the dog isn't being forced to go at too fast a pace for too long.