if it ever gets stolen or damaged in a fire or anything like that the equipment will be replaced at current market value plus interruption of business charges as well.
My thought..... perhaps you should be finding an insurance policy that will pay "replacement cost" for a new unit plus coverage for business income losses (due to miner not being in operation), not the nebulous "market value".
If you go the insurance route; there is a problem that the market value of the unit may very well drop to $0 after the loss occured, but before the months it takes for insurance claim process to finish and pay you out.
Plus you will have lost all that mining revenue.
My first thought.... how to prevent theft......
(1) Get a big 19" cabinet, that has a door with a high-security lock.
(2) Mount the miners in the cabinet.
(3) Rig an inexpensive alarm panel with a siren 20db or higher; some magnetic reed switches in the cabinet; run some wires out of the cabinet, for perhaps an extra motion sensor in the room.
(4) Get some extra heavy-duty chains, and run them around the cabinet; secure with a padlock.
If necessary; drill some holes in the cabinet to mount loops for the chains to go through, or weld them to the cabinet.
(5) Highly visible cameras mounted in high places outdoors
(6) Consider defensive/deterrent systems which emit a Pepper Spray Aerosol when triggered, e.g.
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