There are many forms online setting forth a template for a personal guarantee concerning an obligation owed by a business with respect to its owner or a third party. Some templates can be as simple as a mofidication of a promissory note whose form can be found online.In your situation, I suggest some simple language as follows in a document entitled "Personal Guarantee""I (name) personally guarantee the obligation and debt owed by (name) in the amount of $_______ for work/services/materials provided by (name) and the following address __________ during the period of _______ to ________" and have the document dated and signed by that person giving the guarantee.If you want more detail in the template above, do so and have a stated payment date as well.