Here's a picture:
In the bottom of my oven is a thin aluminum plan (the kind that you buy at the grocery store) covered in aluminum foil. I purchase the extra long roll of foil for this project. I cover the pan and place it in the bottom of my oven.
When something spills, all I have to do is replace the aluminum foil on the tray. Many people put a cookie sheet under things to catch spills. I don't like to do this because it can impede the cooking of the bottom of the pie or other baked food.
Yesterday, my muffins spilled over and the smell of something burning crept into the kitchen. After the oven had cooled, I just pulled the tray out and replaced the foil! Yippee!
I've had self-cleaning ovens before and have tried oven cleaners, but they leave horrible smells. This little trick has saved me a lot headaches!