outdoor portrait question

[TXForesterII]

A friend has asked me to shoot her kids. I'd like to do mostly outdoor locations and use the sun as a hair light and my flash (diffused and off camera) as the main light.

Without buying another flash, I'm stuck with 1/180" as a top sync speed. If I get stuck with a brightly lit background, I need a way to shoot wider than f16 @ iso 100 and still have more control over the exposure for ambient light.

Can I use a ND filter, so I can shoot nearly wide open and have more room to adjust shutter speed to control the ambient light exposure? Are there other options besides sticking to backgrounds that are less ambient light?

Thanks for any help.

[DEMDeepEllumMusic]

Mike go poke around photoflex's website, they have some free lessons on there, and they cover this topic very well and instead of a flash they use a reflector to light their subject up.
Shooting Models Outdoors for Catalog Work

[TXForesterII]

thank you