Slow Shutdown When Connected to Samba Shares

I realize this may be a more general linux issue than Netrunner, but I am interested in your preferred solution:

After I use Netrunner to access shared Samba/Windows partitions at work, when I then later restart or shutdown the machine, it takes much longer than normal (five or six times at least) to complete shutdown or rebooting. I gather that this is some difficulty in shutting down the samba shares, because the problem does not exist if I issue an “umount -a” command as root prior to shutting down.

I also gather this is a fairly common issue (or would be for anyone using Netrunner in a mixed Windows environment) so i thought I’d ask the question. Do you have a preferred method of dealing with this problem? I’ve seen some suggestions about adding scripts to be executed at shutdown but I haven’t found anything that works reliably.

Thanks very much!