Looks nicely made.
However, a $10 Harbor Freight battery powered grinder with a cutoff wheel WILL easily cut that off in 10 seconds..
Aluminum is a poor choice concerning "security"..
Steel would only mildly delay a thief with a battery grinder.
That only keeps the "casual" thief "honest", will not stop or deter DETERMINED thieves.
Best policy is OUT OF SIGHT, OUT OF MIND.
I would suggest either the stealth approach INSIDE a heavy duty steel box or take them with you..