In that case, my answer is the same but more involved. I have personally dealt with people not wanting to detach, and I've been a cop and helped other people with similar situations. This is what I would do. It may or may not be entirely appropriate for your situation. It's not one size fits all, you can take these tips and figure out the best way to apply them to your life.
(1) Let your friend in on your plans so that they can mentally/emotionally/physically prepare themselves. Let them know that you worry about backlash being directed at them. If they do not know about your parent's history, tell them specifically what you are afraid of. What they choose to do with that information is up to them.
(2) Tell your parents in no uncertain terms that you do not want contact with them, that your friend does not want contact with them, and any contact from them whatsoever will be documented and kept in order to demonstrate harassment to law enforcement for the purposes of getting a restraining order.
(3) When you move, don't tell anyone your new address. Including your friend (if they want to hang out, meet for lunch and you can drive them back to your place). There are boxes you can check on certain forms so that your address will remain unlisted.
(4) New phone number, new email address. Again - don't tell anyone that doesn't need to know. If your parents are serious about finding you, they will ask other people. The fewer people that know how to get in touch with you, the better. If possible, don't turn off your old number. It is better if they think you are just not answering.
(5) If you're using social media, assume that your parents have a way to see anything that you post. Turn off things that tag your location or show when you are nearby.
(6) If your parents do track you down, record everything in as much detail as you can. If they show up at your home and you cannot otherwise avoid them, get a camera on them and make a video. I have had unwanted relatives show up at my door before and nothing sends people packing like telling them they're being live streamed.
(7) Ignore other attempts at contact. Each response from you buys another six weeks of contact from them. If you can think of a relative that you trust, give them your email address and tell them that can be used to contact you in the event of death/serious illness/any other reason you would accept contact from your parents.
