Having seen the results of a tethered fuel cap on the external paintwork after a short flight, I don't really think that is the optimal solution. Much cheaper and better to lose the cap.[It is a bit similar to the effect of a seat belt buckle flapping in the breeze]
I have done it more than once; I suspect most pilots have.
It usually occurs when something disrupts your normal procedure, in my experience. Very difficult to entirely prevent such things.
The ultimate is to include something physical that prompts you at the start-up or just before lift-off stages. Even that requires the self-discipline of using the protection.