An overview of cantonal dog rules can be found here:
http://www.tierimrecht.org/de/tiersc...echt/index.php
(New legislation is pending in several cantons; check the cantonal website for the latest information.)
Please be aware that in addition to the cantonal regulations, local authorities may designate areas where dogs are not allowed, or where they must be kept on lead. For instance, dogs are generally not allowed in cemeteries, school grounds and swimming areas, and dogs are generally required to be on lead in
Naturschutz (wildlife refuge) areas, when walking on streets, and in residential areas. During the spring, dogs are usually asked to be re-leashed while in wooded areas to protect young wild animals, ditto during hunting season for your dog's safety.
If there are no signs indicating otherwise, and if the cantonal rules allow, you can pretty much assume that it is OK to let your well behaved dog off lead.
(Stepping on soapbox...

)
Obviously, though, if a dog has anything less than perfect instant recall, he/she should be kept on lead. Standard etiquette asks that if you see an on-lead dog walking towards you, you should recall and re-leash yours. It's always best to ask permission of the owner before allowing your dog to approach another.
If an area is marked as 'on-lead', please do comply. Thanks to the recent tabloid campaign

, there is so much fear, misunderstanding and even hatred towards dogs out there - we don't need to add fuel to the fire. Disregarding local rules only undermines the fight against the draconian legislation now under proposal; responsible ownership is the best way to win hearts and minds.
(Stepping off soapbox now...)
Look what has happened down my way: My favorite walk was through a woods along a parcours; signs clearly asked that dogs be kept on lead. Nonetheless, for years some owners let their dogs run free through the area. Finally the Gemeinde got fed up, and dogs are now banned from the woods altogether.
The police were out one weekend reminding people to keep their dogs off the parcours, and on-lead in the
Naturschutz zone; fines were mentioned, but I have no idea how much.
I wish we had real dog parks here; I'd give anything for a place where my youngster could safely get the off-lead exercise and socialization she needs. Unfortunately, I haven't found one yet. Some dog clubs will rent their training grounds to members for occasional private use; you might try asking your local club if that would be possible. Additionally, some farmers rent out their unused fields.