I had an issue with my children accessing via other devices granted prior to getting teh whole home wifi. The way i got round it was to set up IP addrsses specific to the MAC codes of the device. So only MAC registered devices could work on the network totally cured the borrowing issue.
Also used this for my Foster Families that had children in care whilst I was working as a Social Worker, its protects your network stopping any tom **bleep** or harry trying to log on with your password.
It may help with your request, yes it does take a little while to set up but is well worth the effort.