I don't want to buy my dad a gps tracker to put in my mom's car.
Why do you not want to put the GPS tracker in her car?
Because as a programmer I know all the ways around such devices. It would be easy for me to remove it or even track her.
If you feel that's a risk, or that your dad is trying to spy on her, than it's good of you to stand up for her!  One should hope your parents would have learned to be more trusting by now!
What.
Don't feel coerced into doing something that you are not comfortable with. Talk to your parents and let them know that their trust issues need to be resolved in another manner and to leave you out of it.