Network connections to NAS keep dropping


iMac - os/x 10.8 (up to date)

Regardless of the network protocol, SMB or APF (NFS refuses to connect and is another story), os/x must be manually connected to a remote NAS file server after log-in. Then, after some indeterminate period of time (8 hours? 12 hours? I cannot get a handle on the time frame), os/x arbitrarily ends the connection, usually badly. Then the connection must be manually re-established.

This would be annoying enough. However, after a couple of re-connections, os/x simply cannot successfully re-connect; it sits there like a stunned mullet doing nothing. Sometimes I get a message about a "missing object." Hmph. This indicates that I must now log-out/log-in to clear the stale objects since os/x seems incapable of doing anything sensible at this point. On more rare occasions the log-out fails to complete (nothing but a white screen of death); a re-boot is required.

Other systems (linux, windows, even an os/2) at our site have no such difficulty with any of the protocols or maintaining connections to the same server.

How do I have os/x automatically connect to a remote server at login?
How do I have os/x PERMANENTLY connect to a remote server?
How do I have os/x never drop a connection until I explicitly request it?