i agree, always leash unless you really are somewhere with no traffic (we go unleashed down the beach but as soon as we head back to the carpark the lead goes back on).
a fenced dog park is great to let them off leash. We have large dog parks here and we let them all off leash to play, of course she never listens and comes back in her own time but shes just too busy playing with the other dogs, we know shes safe and shes just got oodles of energy to burn so we let her play as theres just so many dogs to interact/chase/wrestle with etc
The only other time shes ever off leash is at agility/obedience training. Now this isnt a fenced area but its a rather big park before you get to any roads. We do off leash exercises there and we've never had an issue.
It just depends on how reliable your recall is. When she knows its play time at the dog park, thats it (recall goes out the window) until shes tired but if we are at training her recall is perfect and she is zoned into me.
An idea: use longer leads or retractable leads for unfenced areas. when we go walking we have the normal lead to get to the place and once we hit the open paddocks shes on a 5ft long lead (the other half made for me and put a clip on the end so i actually clip it to my belt instead of me holding onto it). Which is plenty enough for her to explore all over the place
but im always cautious, even at the beach if theres birds or anything worth chasing, no amount of calling will get her to come back until the chase is done, then she will look for us. but thats just the nature of the B, they love to hunt/chase things.
thats just my experience