I can answer your question regarding regime for your cat.I have a parasite problem too, so it was essential I kept my cats parasite free for my own sake as well as theirs.
I live in the UK so I don't know if you have the same products available in USA.
Once a month, even thru the winter apply Stronghold pipette to back of neck. externally.
Stronghold is a topical once a month broad spectrum paraside for external and internal parasites. it protects against fleas, heartworm, ear mites, hookworm and round worm.
in addition you need to give your cat a tape worm tablet every 3 months - availble from vet or on line.
This covers 99% of what your cat is likeley to pick up from day to day in the garden. Cats can pick up parasites on a daily basis which is why they need to be treated so frequently with products that maintain their efectiveness over a period of time. treating just once a year is just a waste of time.
its not cheap but essential in your battle to clear yourself!