IIRC it's 36 STR to destroy with a stoneaxe, 25 with a pickaxe.
Destroying a hearthfire on your claim shouldn't leave scents, just double check that criminal acts is off when you do it to guarantee scents aren't left.
Soak is 5, so you need 25 with a stone axe, 16 with a pick, and 4 with a sledge.
(soak + 1 - tool damage) squared to figure how much damage you need to break something. soak can be looked up on the RoB wiki for the item in question: http://www.ringofbrodgar.com/
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