Thanks for your answer, though This was not what I expected.
I have not bought fences for paying a wallpaper that I don't want. I already had one that I love.
I would have been great if it could have been written somewhere before buying fences.
You couldn't use a live wallpaper if you use Fences... So simple and I would have not thought of a kind of trap...
PS : Perhaps could I hope of an update that would answer this....