Does anyone have a home-made solution for fleas/ticks?

One of my dogs has a lot of fleas and ticks. The other one doesn’t have any funnily enough. I need to frontline him almost every week and it still doesn’t work. Front-line spray and flea shampoo is chemical obviously, I’m wondering how it will effect him if I do it so frequently? He is old and I’m sure these are pesticide based, I don’t like spraying him all the time. Is there any natural or home made solution to fleas and ticks?