2x Preventic 25" Tick Collar for Dogs up to 4 Months Kills & Detaches Ticks Provides full protection against ticks within 48 hours of placement. Stops new ticks from attaching. Demonstrated 92% efficacy in controlling a severe tick infestation after 24 hoursversus 63% efficacy achieved by a deltamethrin collar. Paralyzes tick mouth parts to prevent feeding. Water-resistantEffectiveness is not diminished if the dog gets wet. Collar sizes available25 for any size.