First, an agreement drawn by parties without the aid of attorneys is generally fraught with problems. Lay persons ordinarily are not sufficiently able to draft agreements to state precisely what is intended. In the case of the question above, where only one party has an attorney, it is particularly important for the party without an attorney to consult with a lawyer who can provide advice regarding the proposal. It is important to retain counsel to avoid being taken advantage of, however, another reason, perhaps not as obvious, is the unfortunate reality that many attorneys write agreements haphazardly and without sufficient case. Indeed, if you hire an experienced attorney, it may actually benefit both you and your ex.
If you, on the other hand, have retained an attorney but your ex has not done so, you may believe that it is open season and you are sure to come out on the better end, however, be aware that the victory may be short-lived. An agreement entered into without the aid of a separate attorney representing each is frequently subject to being later set aside upon the claim the unrepresented party failed to understand the legal consequences of the provisions within the agreement.