Fixing pressure cracks and collision cracks

Hey Everyone, After searching for about 45 minutes I can’t find anything. I’ve got a few pressure cracks on my board near the rail. It’s a sand finished longboard that has one crack from my taking it in the chin on a small close out and another from a kook bailing off his board in 2 foot surf. ANYHOW… I’m going to work on fixing them today and in the past I’ve been able to fix full out dings that need filler and what not, but have yet to figure out how to fix the crack so that it appears invisible. What is the technique and needed tools to do so? I’ve heard something about slicing perpendicular to the crack to create an entrance for the resin, but I’ve only seen this method told once so I’m not so sure on it. Any and all help is appreciated. Christian