I have worn the following goggles for 20 years.

Speedo Pro Anti-Fog:

http://www.speedousa.com/index.cfm/f...-0148ac9dd5e3/

They are just normal goggles. I've worn them in all my races for 4 years. Never once have I worried about getting them knocked off my head. They work for me.

Also, you can put the strap of the goggles under your swim cap if you are worried about them getting knocked off.