If it is "meine" for feminine and "mein" for masculine, then it should be "meine rock".
No, because the noun Rock is masculine.
The form meine or mein depends on the grammatical gender of the following noun, not on the natural gender of the owner.
Also, since Rock is a noun, it has to be capitalised; rock is just as wrong as, say, Ruck.
When did men start wearing skirts?
Is there a good way to know what is masculine and feminine in german?
No, not in general.
You basically always have to look it up in a dictionary and memorise the result.
Same with plural forms: those are also mostly memorisation.
(Some words even have multiple genders, and/or multiple plural forms, depending on the meaning!)