Have you talked to your vet to see if they have any suggestions???

Honestly I don't know what to suggest. I, personally don't think Frontline works well for Ticks (atleast not in my experience).... and luckily I've never had huge tick problems like you are dealing with.

The last vet clinic I worked out, we used a shampoo called Ectokyl http://www.healthypets.com/ectokylca8oz.html.
I guess its the best flea/tick shampoo I've seen... but I HATED using this shampoo because it really bothered my skin..... anytime I used it on dogs at work my arms always broke out in really red rashes...

You could try this.. your vet might sell it....

Janna