HelloCustomer thank you so much for your question! I hope I can be of help to you.
Aspirin certainly can be used for dogs, and the correct dose in approximately 5 milligrams per pound of body weight. Baby aspirin (81 mg) or adult buffered aspirin (325 mg) are the best options, and they can be split to be dosed as accurately as possible.
Here is some additional information on aspirin usage in dogs:
Please be sure your dog does not have any pre-existing conditions such as kidney issues that would be aspirin use a bad idea. As well, aspirin should never be used in addition to other anti-inflammatories such as prednisone (steroids) or other pain relief meds from your vet.
I hope this helps. Please let me know if you have any additional questions! Dr. Marcia
* I just saw your additional notes about your dogs busy day at the park! Aspirin should be helpful, and can be repeated up to twice daily over the weekend. If the leg is not improving, be sure to have it checked out next week. Thanks!