The attorney's job is to reach a split that both parites agree to and the court's job is to approve a divorce settlement that is equitable (which does not always mean "fair" or equal). So, most attorneys will attempt to make it as equitable as possible knowing that the court may not approve a settlement if it is not.
There are different rules in different states about what is separate property, what is marital property, how separate property can become marital property, etc. and that all plays into the split in a divorce.
At the end of the day, your spouse can ask for anything s/he wants, but that doesn't mean s/he will get it, and you can agree to split things up, more or less, any way that you want. For example, if you have a paid off house worth $500,000 and your 401k is worth $500K, you could potentially work it out where you keep all of your 401k and s/he gets the house. And genearlly, as long as the assets and/or debts are split equitably, that will usually suffice.
All of that being said, since this is a legal question, you need to talk to an attorney that deals with divorces. And be sure to let him/her know exactly what you want as far as assets, etc. - it doesn't mean it will work out exactly like that, but if you don't communicate your wishes, then it is probably that it definitely won't work out how you want.
Hope that helps and best of luck.