Who pays for locks - landlord or tenant?

[Bruce Chang]

Who pays for the lock if tenants continue to keep breaking the lock?  Our family has a duplex, and the lock on the security gate has been fixed and broken several times.  Tenants point fingers at each other and neither take responsibility for breaking the lock.   Can we have the tenants split the cost of any future repairs or do we even bother fixing the security gate at all?  Front doors of both units have working dead bolts.  There is nothing in the lease that says the tenant needs to pay for a broken lock.