Seems like a waste, but you could probably cut sap with some cheap rum or bourbon. Likely not to be quite so hazardous for the pooch then either.

Or you could just rub some meat broth on it and the dog will get rid of the sap himself.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)