SBA 504 loans are typically secured by a lien on fixed assets acquired with loan proceeds to reasonably assure loan repayment. 

The SBA's lien is subordinate to the private lender's position.

In addition, the SBA requires the personal guaranties of the principal with 20% or more ownership and/or a key management position. Owners/principals with between 5% and 20% ownership may be required to guarantee, as well.