How can I establish circumstance(s) that terminate spousal support?

If you would like the spousal support obligation to last for four years, for example, the clause would read something like the following:

The husband agrees to pay to the wife for her support and as spousal support under state and federal law the amount of $XX per week, starting on the first Monday following the execution of this agreement and payable thereafter on the same day of each week.

The payment shall cease upon the death of the husband or the wife, the wife’s remarriage, or after 208 consecutive weekly payments, whichever comes first.