I wouldn't use lemon. It's just not going to work, and why put in all the effort.
There are a lot of flea/tick prevention options out there and I think that is really the only thing that is going to help.
Seresto, Nexgard, Bravecto, Credelio, Advantix
You are going to need to apply/administer the medication for at least 3 months (flea life cycle) and vacuum every day.
You don't say the size of your dog, but a quick search on Chewy shows that Nexgard in the highest weight range would cost $72 for 3 chews.
Credelio $117 for a 6 month supply (again for the largest weight range) and
Bravecto $68 for 1 chew that lasts 3 months
Most Vet clinics will let you buy one chew/tube at a time as well.