When Gerona was a baby, she would dart outside the door when you opened it (from the outside). She gave me so many scares it's amazing I don't have a grey hair from her! At first I could rattle her jingle balls and throw them in the house and she'd go darting in after them. But then, she got too smart for that. I started using my brother's rat terrier (whom she loved to play with) as a means of a decoy to get her out of the bushes or tree so I could snatch her up.
I'm SO glad that a) she doesn't door-dart anymore and b) we have two doors leading to the outside (have to go through the mudroom) so if she door darts the first time, you can catch her in the mudroom.
I took Gerona for a walk outside one day here and she slipped her collar. I was about to pee on myself I was so scared. Thankfully, she got stuck in some bushes and I grabbed her tail before she could slip through.
So, Carmen, I say YES to the harness. It's amazing how easy the cats can slip from their collars. Also, make sure the harness is a bit snug. They can sometimes slip from those, too, if they're clever enough.
Hopefully you won't have another scare like this.
I know how terrifying they can me ... And don't you just want to BEAT them when you finally catch them?
How dare they scare the dickens out of you!