Thanks! But I prefer not to install beta versions! After a couple of times, the context menu option 'Activate Fences' finally worked but the 3 fences I had created were empty ! And all other icons on my desktop that were not part of any fence have disappeared!!
I've uninstalled Fences today (and purged the files as mentionned in the link provided) and I'm going to re-install it. I'm back as soon as it'll be done to give feedback...