Shawn Lagemann If you look at this picture closely, you can see that the planters are not against the fence. To protect a wood planter box from rot, you use black pond liner that is sealed against the top trim so moisture is less likely to get in between causing rot. Anything placed up against a wood fence can hold moisture against the wood causing decay. Replacing a few pickets may not be a big deal, but replcing rotted posts iis real pain. The only suggestion would be to raise the dirt level first and install the fence on that level.