zfs set snapdir=hidden
For example:
server:# ls -al .
total 4335
drwxr-xr-x 10 root 532 22 Jan 4 2008 .
drwxr-xr-x 101 root root 100 Mar 28 09:46 ..
dr-xr-xr-x 3 root root 3 Dec 13 2010 .zfs
...
zfs set snapdir=hidden (current/zfs/filesystem)
server:# ls -al .
total 4335
drwxr-xr-x 10 root 532 22 Jan 4 2008 .
drwxr-xr-x 101 root root 100 Mar 28 09:46 ..
...
As you can see '.zfs' directory is hidden. Despite this fact you can always get into this directory (remember - it is hidden, not removed !) and use it :-)