How do you tie users to devices (automagically)?

How do you tie users to devices (automagically)?

We use the full SDP and DC suite (on-prem).  We continue to struggle with asset management, even after trying to use SDP and DC for it (separately).  

We have 2 separate issues:

1.  Computer A changes hands, with or without IT involvement.  User is not updated manually for the device.  Any way to have the device update it's "owner" in the system?

2.  Computer A gets shoved in a drawer and forgotten about for 120 days.  We remove PC's from DC after 30 days which is great for licensing management.  At 31 days, we have essentially "lost" a device and it is forgotten about.  

How does everyone else do this?  Our process has plenty of holes in it and we would like to improve this process.