Lockouts ...what do you do?

Tenancy Deposits

I have 3 bedroomed shared houses let to young professionals. Each tenant has a lockable bedroom door with Yale lock.Contract states firm procedure in cases of misplaced keys, bedroom lockouts and invites tenants to secrete spare door key in a place only known to them.They are given a spare for this purpose.

Often I am called [28 mile round trip]to admit a tenant to a house or to their room because they've locked themselves out. I only once did not jump to immediately rush there and I found damaged locks/architrave etc from forced entry to the bedroom.
I manage the properties myself and take pride in an out of hours flexible service,however, this is often severely tested at my holiday periods, Xmas time, family celebration time, or at 4am in the morning.

I'm asking colleagues what tactics they use to reduce or avoid this thorny issue of tenant'lockouts'. An agent's service would provide office hours cover. I provide much more cover than this but state that call out charges [£15]are applied to cover my expenses. This does not prevent carelessness.

Has anyone got any tips to pass on - or will this request for advice wither on the vinelike the others I have posted. You will find that I often reply to colleages queries, dare i expect the same courtesy?