Starting April 1st, dogs must be kept on a leash at all times and are never to be left unattended. This to prevent them from disturbing the wildlife, including barking at wildlife, in the cantons of Aargau, Lucerne, and Zug. For the canton of Zurich please pay attention to signposting.
This is in effect till July 31st in and close to forests. Also, the dogs are not allowed to play on agricultural land till October 31st, if the grass is taller than 6 inches/15 cm.