Although I have started wearing a helmet more when I ride, I do have stampede strings in all my cowboy hats. I like the cotter pin type. There are some pretty cool ones out there. I have several made of kangaroo and some horsehair ones that are very pretty.
The cotter pin type are almost like sticking a large needle through the hat liner/band.
If your hat has no liner/band, I think your better off with the string type.
Here is a site with a photo adding a string type. I have ordered from this site before, they have good quality stuff if your interested.
http://www.outwestsaddlery.com/html/...e_strings.html