I need a VERY, very fragrant plant?

I have a 16' x 20' backyard patio I would like to use more often for lounging and/or outdoor dining. The trouble is it is downwind from our septic system's exhaust pipe...which means whiffs of unpleasant sewer odors once in a while. The pipe is far enough away that the odors aren't strong or constant, fortunately, but they're still noticeable any time someone runs water in the house. I was hoping to camouflage the odors by planting some intensely aromatic shrubs. I really don't care WHAT kind of plant -- just that it is highly fragrant and that it be perennial. The plant needs to be able to tolerate variable sun/shade conditions as well as somewhat sandy soil, and shouldn't grow too large -- maybe about the size of a Nandina. I live in Zone 7. Any suggestions?