You don't have to walk all around the yard or house doing these. You could modify them by finding the longest space I could (a hallway, as others have suggested, or the length of a room), then doing as many forward as I can, turn around and go back the other way. Just make sure that you can either do an even number both ways, or if it's an odd number, start each pass with the opposite leg, to make sure to do the same number of reps for each leg. You could also do several forward walking lunges, then without turning around, return to the beginning doing rear lunges.