Keeping Fruit Down in Primary

Going to use blood oranges and peels in a straining bag in primary which is a 6 gallon plastic carboy. I've read that they float and that can get it to grow mold. What a good object to throw in the bag with the oranges to keep them from floating. Don't want any off flavors or contamination risk and since I'm still new to brewing I'm not sure what is good or bad to throw in there.

*edit* Grammar and spelling corrections. Using phone and typed in some odd words

If you had a smooth polished stone soaked in sanitizer for a bit, I imagine that would work well. Stainless steel ball bearings or nuts would work too.

Anything bad about throwing a sterilized spoon in the bag with the fruit?

As long as it's stainless steel, you should be fine.

Glass marbles.