I smoked up in my living room with a bunch of friends for a couple weeks while my parents were gone in florida. The couches pretty much soaked up the THC fumes and they were slowly coming out into the air.. I was constantly buzzing for about 3 days after a toke session. It was the middle of the summer. Point being, don't smoke around stuff that could soak up the smell and wont get washed by the time they get back. Heheh.
You'll be fine if your parents aren't home. I used to smoke in my room and the car all the time and the next day it never smelled. Ozium is what I used at boarding school.. I used to smoke out of a one hitter or a one hitter bong, hold the hit in real long and blow it out the window... then if it smelled I would spray some ozium and be good to go. Incense works good, but its kinda shady and I wasn't able to use it at school. A lot of adults when they were our age used incense to cover up weed smoke so in a lot of cases you incriminate yourself using it. When I was at home I would use it for meditation... I don't think it does the best job of covering up herb.