I have a basic Yale alarm which emits a horrendous noise if you accidentally set it off.
Builders band securing the roof to the sides (usually easily lifted off for access) and securing the sides to each other.
Two bits of bent rebar set into the concrete base with decent motorcycle chain locks securing the bikes.
Security / coach boots on all the hinges etc.
Half decent padlock on a hasp and staple.
Solar floodlights activated by movement.
Decent insurance policy.