For obvious reasons, commercial landlords routinely insist that a commercial tenant provide a personal guaranty of the payment and performance obligations of the tenant.  It is not surprising that litigation often arises between the landlord and the guarantor upon the default by the tenant with a common defense being that the terms of the guaranty were not intended to cover the specific default at issue.  

The general rule is that a personal guaranty is to be strictly construed and a "guarantor should not be bound beyond the express terms of his guarantee."  As a result, to help ensure maximum security, it is common for landlords to require that a guaranty provide that it is applicable to any "renewal, change or extension of the Lease."  Despite such broad language, there is much litigation over whether the particular guaranty is enforceable when leases are renewed, extended or changed.