How do I instate a prenuptial agreement when common law (or legally) married in Texas?

first, you cannot have a prenuptial agreement after you are married. This type of agreement is entered into prior to marriage. You would be interested in a post-nuptial agreement, and your options will be slightly more limited.

More importantly, for what you are trying to accomplish, you dont really need an agreement. Your husband is not entitled to any of the funds you would receive through a will. Getting money or property through a will is considered separate property and not part of the community estate.

For example, lets say you got a million dollars from your grandparents after they passed away as a result of their will. And you deposit that million dollars in a savings account. A year later, you divorce. Your husband is not entitled to any portion of the million dollars as community property. He is, however, entitled to his share of the interest gained from that money. Basically, any money you make during the marriage is considered community property, but property you receive by gift, devise, or descent (through a will), is not considered community property.

I hope this makes sense....