My dog contracted Lyme while she was on Frontline Plus. I now use the Preventic collar (only when we are out tracking).
Also, use common sense- check over your dogs skin daily, especially if you have been in areas with tall grasses or dense undergrowth. Use a flea comb to comb the fur backwards to look at the skin. Especially check warm areas like the neck, head, ears, armpits, belly and anus.
An infected deer tick needs to be attached for 48 hours to transmit the Lyme spirochete to your dog. It won't get the disease if the tick just bites but does not attach for that duration. Also, this time of year the deer ticks are in their nymph stage, and are usually attaching to smaller hosts like mice. Its the fall when they become a bigger problem for the dogs (and deer). Right now you're likely to pick up some of the larger American Dog Ticks, which do not carry the Lyme spirochette.
Here's a link with some info:
Lyme Disease