DonC "Not sure what a long day in the park is"
No, nor am I, but I do know that after even an hour racing around in the woods, my dogs need sleep ! Basenjis do sleep for long periods after strenuous exercise and I know mine would all have been exhausted after a long day out in a park.
If you can find a vet who does acupuncture, can first make a diagnosis and then if it is indicated, go on to perform acu - that is the best option. If not, first talk to your normal vet and, if he doesn't do acupuncture, see if you can get a referral to one who does.
I use CBD oil for my old folk - being careful to get a good quality, reliable one. In this country Woods (on line) sells a very high grade especially for dogs. Hoover (12) and before her Keepurr aged 13 noticeably benefitted from it. Hoover also gets acupuncture from our own vet - and he figured out the right CBD oil doseage for her too. But she has a very specific joint problem, revealed by X-rays.
Over the years, many of my Basenjis have received acupuncture - the first of our vets to administer it - sadly no longer with us but I'm sure treating animals beyond the Rainbow Bridge, called it 'geriatric juice'. The oldies all showed improvement, but they weren't acually started on it until they were 10, 11 or even teenagers.
Good luck and let us know how it goes