Actually, after the 1.34 patch you can lockpick the Nericon Garden gate, though that may lead to a broken quest or missed experience points if you do so before getting the key. Before the patch, a few people lost the key, by using it on the cemetery gate. There is also a key to either gate in the potion dealer's house in Ars Magicana, though it is tricky to get into his back rooms.
