Yeah, I figured you'd not know because you don't live in Australia and have firearms.

I wonder how they are able to check and enforce that

With random and unannounced checks from the firearms branch of the police force. Part of having a firearms license is the inability to refuse entry to the firearms branch and their spot checks.

It's going to be difficult for you have any comprehension of the laws here because you're not here; furthermore, most people have literally no idea about the laws around firearms even if they live here in Australia.