Hi
Did you use the spray or spot on's? Its very important that you adminster either of these as guided by the packet. Often when people say that it hasn't worked is due to incorrect appilcation, If it's the spot on used you have to get it on the skin and not the fur as not enough is distributed around, at work we recomend that you apply it in 2/3 spot around the shoulder area as there is quite alot to get on and with the spray you really need to sodden them. Do you mean Staykill not stronghold for the house? You need to be quite librial with your use, obviously paying good attention to the areas most frequented by the animals but also its a good idea to pay good attention under furniture such as Seatees, chairs, under TV, fridge, freezer, washing machine, etc... as they imgrate to warm areas.
I forgot Frontline can take up to 24 hrs to get to effectiveness
HTH