We just moved here and I am wondering : What to plant over the septic field?

We just cleaned out the septic field (see where the Halloween decor is). I put this picture in so you see I can not add it to the house landscaping...Ugg...we have clay, so the house landscaping will have to probably wait 'till fall (we have salt water-can not water with house water) So, for now I'm just concern what type of decoration or planting should I put in the area right over the clean out. We can not just grass it over because we need to be able to find it again when we clean out again. Any suggestions? Thanks

Original article and pictures take http://www.hometalk.com/1188103/we-just-moved-here-and-i-am-wondering-what-to-plant-over-the-septic-field site