No matter what treatment you use, the tick must still bite the animal in order to get the treatment.
And yes, they can still transmit diseases. Treating pets lessens the risk considerably for the pet and the people though, and if they drop off the pet, then it's a doomed tick anyway, as the poison will be effective at killing them, but it doesn't happen right away.
Doubling up on preventatives though could pose risks for your dog, just be aware of that too.
Herb only treatment for Lyme & Bart ended 12/11 - no active symptoms for 2 yrs -Herb only treatment for Babesia ended 12/12www.healingwell.com/community/default.aspx?f=30&m=2977364
Had Lyme, Bart, Babs, RMSF, Ehrlichia, Myco, Anaplasmosis, EBV
New Lyme case 8/2014 - Healed 1/31/15 - unknowingly had Asymptomatic Babs and Asymptomatic Bart, being treated now though (2/2016)