I found that if the Seresto collar gets wet, it is not effective. Check the instructions about that.
For years I used Frontline Plus which is a topical. The patent for Frontline Plus has expired, so you can get the main ingredient, fibronil, for less money in other products. I use Pet Action Plus from Sam's club.
In the spring and fall when ticks are most active I also use a flea and tick collar. It is called Preventix and is about $17 at Tractor Supply. I found it to be very effective.