There is a lot online regarding this subject. If you feel like it is a "risk" to have another child because it might not be a boy, it is still your decision to make and no one should judge you. As loving parents of 3 beautiful daughters surely you will feel blessed even to receive another baby girl to cherish. Here is one article I read.
http://***********************/Faqs/Gender-Selection-Methods---Scientific-Evidence.html
But there are many stories online of pleased parents who got the gender they most desired from a method they feel works.
In the end you still get a beautiful child to love and raise. Although I hope you guys get the little boy you're hoping for. Congratulations either way!
Have sex on the day you ovulate and you will have a boy :) it works. It has worked for many of my friends and you can read articles about this on the Internet. I am planning to conceive and we want a boy. I am going to have sex on the day I ovulate.