Search through the internet. What you want to look for is a unit that's capable of leaving a popcorn trail as you go about your wheeling. You can store these popcorn trail in the memory and name it so when you want to find your way back on the same trail, you can pull up that last route and follow it. I've used the GPS-18 on my laptop to map out the trails and locations of the deer blinds in the ranch using the popcorn trail feature and along the way, i've marked out alternative trails as well but if a laptop is too bulky for you , there's unit's out there that will do the same in a more compact package.
BTW, i moved your thread on the electronics section.