Yes of course, if you use the
setPos command (thats a link to the comref there) to place a SECOND fence above your first fence it means you get a sort of 'double fence' effect, you can use as many fences as you like and you'll have to experiment with the z variable to get the right height.
If you have trouble getting it placed exactly on top of the lower fence you can use
getPos like this example ...
_topheight = 0.8
fencehigh setpos [getPos fencelow select 0, getPos fencelow select 1, (getPos fencelow select 2)+_topheight]
Where 'fencehigh' and 'fencelow' are the names of the respective fences.
Obviously change the variable _topheight to adjust how high you want the second fence to be. If you want you can stick the above code in the init code line of the higher fence in the editor but remember
1) Name the lower fence so you can refer to it.
2) Just replace '+_topheight' with '+' and then your number.
3) Change 'fencelow' to 'this'
Hope this solves your problemo