Offroad Garmin

I have a couple of Garmin Nuvi units that I use regularly. One is in my work truck because I go all over North Carolina, Virginia, and a few other states. The other is for personal trips. I really like the simplicity of them, and have found them very dependable.
My question is on units designed for offroad use. I haven't used a handheld before, and would like some guidance from people who are familiar with them. I plan to use it for ATV trail riding, hiking, and mountain biking in the southeast region.
Although I don't mind a reasonable investment, I would prefer to focus on keeping it simple and dependable.
Whatever advise you can offer would be appreciated.

Thanks, and Merry Christmas