I think you are looking for the soft mount option. Not sure on OSX but it might be the '-s' flag on the mount command. If not, according to this, you should try:
This sets up a standard unix nfs mount, which is presumably what you want if
you are reading this. Note that you most likely need to run the Repair
Privileges utility first.
Launch netinfo manager and authenticate
from menubar: Directory>New Subdirectory (cmd-n)
Enter the nfs mount path into the value field (eg tao:/home/tao/salathe.
You can find correct root for the volume by typing df on another unix
system where the disk is mounted; it is the first column. You can add
subdirectories to the path)
from menubar: Directory->Append property enter "vfstype" in the property
field and "nfs" in the value(s) field.
Append property dir with value of mounting point (eg /tao) this directory
Append property opts with value -b (to background mount if it fails)
Append value -P (NFS reserved port assignment)
Append value -s (soft mount; mount process will fail after a certain number of tries)
Should have something that looks like:
opts (-b, -P, -s)
Save and quit
Now you need to restart the nfs daemons. Find the pids and "kill -HUP" them. From the shell,
% sudo -s
% ps -aux | grep -E "nfsiod|automount"
root 241 0.0 0.0 1276 84 ?? S 0:00.03 nfsiod -n 4
root 242 0.0 0.0 1276 84 ?? S 0:00.00 nfsiod -n 4
root 243 0.0 0.0 1276 84 ?? S 0:00.00 nfsiod -n 4
root 244 0.0 0.0 1276 84 ?? S 0:00.00 nfsiod -n 4
root 251 0.0 0.1 2392 440 ?? Ss 0:00.08 automount -m /Netwo
root 413 0.0 0.0 1112 196 std R+ 0:00.00 grep -E nfsiod|auto
% kill -HUP 241 242 243 244 251 [or whatever the pids]
Note: Sometimes when the computer goes to sleep and wakes up, mounted
volumes are not fully accessible from Finder. They are still there at
command line. To fix this, use the "force quit" feature to restart Finder.