If you are talking something like this http://www.bluegrassnursery.com/...bhouse-pkg-ii-basic/. Don't worry about securing it will be fine for many years, at least mine hasn't had issue and my son and his friends played on it until he was 9 or 10, when it was 6 years old.

Have fun with the setup, I found you need at least 2 dozen beer 3 friends, and 2 days. Getting a bit that allows you to use a socket with your drill was a life saver, and has come in handy several times since.

Ben