Topband: Resonant frequency of a grounded tower

[Charles Bibb]

I want to determine the resonant frequency of my grounded 90' tower 
with KT-34XA tribander on top.  Looking in the fourth edition of 
ON4UN's book, I see that he suggests running a parallel shunt wire 
down from the top, then grid-dipping the wire.

Is there an easier way?

73,
Charles - K5ZK