Secure as in "inaccessible to minors or unauthorized persons".
I would say a biometric lock (code or fingerprint) on a closet door with a blink or simpli safe camera inside set on motion activation would be sufficient. Add a gun safe bolted to some studs to make it more secure.
You gonna pay for that?
And again... Kids don't have access to angle grinders?
Gonna do anything about the hood rats and mia familia?