lubuntu 12.10, home wireless net environment, Synology NAS

I have a NAS drive that has a scheduled start/shutdown to roughly coincide when we are at home. The NAS holds photos and music, and generally just is used for reads. My laptop automounts two shares on the NAS via nfs.

Problem is that if the NAS shuts down while my laptop is running, file manager just hangs and I can't do any saves/open of local laptop files from any applications. Shutting the laptop down causes shutdown to hang. Running 'mount' from terminal when the NAS box has shutdown shows the NAS mounts still there. Running 'sudo umount [nas mount]' just hangs.

I've read/re-read the nfs docs and googles, and thought I had it sussed, and have I've tried several things but can't solve this prob. Does anyone know how can I make the nfs mounted shares unmount gracefully if/when the NAS 'dies'??

The nfs mount statement in fstab is:
DISKSTATION:/volume1/Photos /mnt/NAS_Photos nfs _netdev,intr,timeo=5,retrans=28,bg,rsize=8192,wsiz e=8192,atime,auto,rw,dev,exec,suid 0 0

'mount' reports:
DISKSTATION:/volume1/Photos on /mnt/NAS_Photos type nfs (rw,intr,timeo=5,retrans=28,bg,rsize=8192,wsize=81 92,addr=,_netdev)