This strong cord is what we recommend to suspend your tarp. It offers good grip on trees, making it the perfect go-to ridge line rope but can also be put to a variety of camping uses.
We at Wylies Outdoor World find 6m of rope is the happy medium for suspending a tarp which leaves you with the option of using the extra 4m for anything you require.
Note: Please ensure the cord is thoroughly dry before storing away with the rest of your gear.