I have a 6 month old puppy, vet gave me Frontline for fleas and ticks and I have been applying it once a month as directed. Yesterday morning I applied it but it rained later that day so he was drizzled on and shortly after that my family played with him and petted him a lot. I feel like it all got rubbed off before it really started spreading throughout his coat. Should I re-apply it to make sure? Is that okay for him? Would it help at all?