I see that even though your wife wants this dog, the favor of God is upon you to stand your ground for truth in this particular situation.
You’re trying to take care of this problem little by little with the ticks, but it’s almost like the “casting of your pearls before swine…”
It turns against you.
This may also be a lingering situation as you have now gotten a cart to pull it behind you.
Like dragging some of the past around.
Any time we compromise the Word, or what we know to be right, eventually it will turn and bite us.
Trust God’s favor through you towards your wife to see truth. Pray that the eyes of her understanding are enlightened to this situation, and believe that As for you and your house, you will serve the Lord and be a light to others around you. Including your father in law. Just keep loving him. Love doesn’t just mean telling people what they want to hear. Jesus is Love and He is The TRUTH!