Require physical delivery of the commodity to the holder of the contract.
To take a related example, if you had a contract for 1000 pork bellies, and couldn't sell them, your lawn would be disgusting (apologies to Dave Barry). Cheers!
So if I'm an oil producer and the price falls below my cost of production, I'm not allowed to sell oil futures to maintain my income?
Leave the bellies in the freezer forever, if you like, as long as you pay the monthly storage/insurance (the 'carry').
What happens in most cases, of course, is that the person receiving delivery either pays a fee to re-deliver, or pays 1 month's carry (in the spring) and sells the next month's futures, intending to deliver back the bellies at that point.
Tch, tch for that silly old canard about a yardfull of wheat or a yardfull of bellies.
But at least it would repel Islamist terrorists.