Naturally repellant

I am keen to find a natural supplement to give to my two Border Collies to help repel fleas and ticks. I have recently bought CSJ Billy No Mates which is great but one of my dogs will not eat it as it has Mint in. The smell puts him off totally. I have heard that Neem is very good, but I am finding it difficult to find out the best way to safely administer it. I also give my dogs other supplements, for example; G-Paws for joints and Beau Oil for coat and skin. I've even considered baking my own dog biscuits and adding Billy No Mates that way but I am unsure whether the cooking will devalue the strength of the supplement? Please can you advise on anything suitable for this problem.
Emma

Gosh - I must look up Billy No Mates, never seen that product before! Any one got any hints for Emma?