Take a look at Australian Cattle dogs. They're smaller than your rhodesian but if you want a dog that you can trust off leash while running or MTBing they're tuff to beat. Negatives they're too smart. that and some masters get creeped out due to the dogs tend to STARE at their masters waiting for orders! My wife can't go any where with out Cole our ACD following! If she goes to the restroom he waits outside the door for her.
They can be a little barky. I can tell what is going on due to Coles bark. He has a great bark for my extended family. another for my sons, a bark for some close friends of ours the mailman/ups bark, a bark for other dogs being walked by, a bark for HEY JIM!!!! this racoon doesn't belong in MY back yard. Joanna has MS and falls. He will run over to her and stand guard over her letting us know she's down! ACD's are not a beginers dog they will test you. I've raised Huskys and Sheltys and Cole has been a handfull but for being a dog he's a great dog.
Australian Cattle Dog - Wikipedia, the free encyclopedia