The Texas Constitution already has it.
Sec. 23. RIGHT TO KEEP AND BEAR ARMS. Every citizen shall have the right to keep and bear arms in the lawful defense of himself or the State; but the Legislature shall have power, by law, to regulate the wearing of arms, with a view to prevent crime.
Not ideal, I would say... but significantly more clear than the US Constitution’s Second Amendment.
Pennsylvania
Right to Bear Arms
Section 21.
The right of the citizens to bear arms in defense of themselves and the State shall not be questioned.