Check out these Gate Closing Springs they sell at Lowes Home Improvement Tim! They cost only $5.67 each and look like they'd do the job well. I suggest using one on both ends if your using it on a really long dipole like a doublet, zepp, or double-extended zepp.

https://www.lowes.com/pd/Hillman-12-in-Zinc-Gate-Extension-Spring/3115909

Very 73,
Cliff, KU4GW