Kenwood deck mounting help?

So I bought a Kenwood deck from my friend. I had noticed that my stock deck was bolted on. And that I had no idea how to bolt my new deck down so it doesnt come out. So basically you can just grab the deck and pull it out. I was wondering how. Or what I can buy so I can mount this deck so it wont come out. The deck fits fine, It stays in.just when I tug on the auxiliary cord or when I pull it. It just come out. Is their a way I can stop this? If so so what must I buy or do? I'm still new at this stuff so I'm confused.and I didn't go to a shop because their were going to overcharge me to install it.