Disable automount where volume is already mounted?

I am running 10.6.2 Server. Is anyone aware of a way I can disable automounting of a home directory when the volume is already mounted? Situation: I have two Xserves, one is a directory and file server, the 2nd is a compute server. I also have a series of Mac laptops. I specified an (afp hosted) network home directory in Workgroup Manager for each user, because we are using Portable Home Directories to maintain sync between the laptops and the user's home directory on the (directory and file-) server. User home directories are located on an XSan volume which is permanently mounted on both servers (with acfs). My problem is the following: When a user logs into the compute server, his home directory is automounted on this machine even though this directory is already available to the machine through the XSan mount. For example, in the result of the mount command below, you can see that /Volumes/arve(/users) is already mounted, and that the automounter has also mounted /Volumes/arve/users when the user logged in. admin@grkapmac8:~/> mount /dev/disk2 on / (hfs, local, journaled) devfs on /dev (devfs, local, nobrowse) /dev/disk3s2 on /Volumes/scratch (hfs, local, journaled) /dev/disk7 on /Volumes/arve (acfs, local) afp_4CklDY4dyApk4Cs3qI0ykk2M-1.2e000008 on /Volumes/arve/users (afpfs, nodev, nosuid, automounted, nobrowse, mounted by jkaplan) This "double mounting" creates havoc with permissions and causes no end to other potential problems. The problem seems to be new to Snow Leopard Server, as I had exactly the same setup with 10.5 Server and never had this problem of double mounting. Can any one tell me how I might keep the user home directories mount point from mounting on the compute server, or at least disable automounting completely on this machine? Thanks very much for any help! Jed