Can you make financial agreements before getting married?

I have been almost religiously saving at least a third of my paychecks each month (sometimes even half of it) for the past 8 years for a down payment on a dream house.Still not entirely there, but at this point, it's gotten to be quite a sum. Anyway, I have been in a serious relationship with a girl the past two years, and we are discussing marriage. I told my dad about it, and he said, "If it doesn't work out and she wants a divorce, you can kiss that savings account you have bye bye--half of it winds up going to her, the other half to a good lawyer to keep her from getting the rest of your stuff. And if you actually do end up buying a house and she wants to get a divorce, it could happen that the judge gives it to her AND you end up paying her monthly payments. And God forbid you end up having children!"

I told him if it was MY money before we married, if the mortgage is in MY name, the car and whatever is paid for by ME and in MY name, why do I have to give it to her just because she wants to leave? His response was "Yeah, tell that to the judge. There are actually women out there who go around marrying wealthy men and then divorcing them for the sole purpose of getting half of what they have."

NOW I'm nervous! Is it possible to make a legal agreement before we get married that states that if she decides to leave, she walks away with only what is HERS and not mine (AND NO MONTHLY PAYMENTS)? I don't see how that is fair at all!

(I'm only 25, so cut a little slack)

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