It’s not a question of whether the Rock the Garden concert, scheduled for June 20 this year outside the Walker Center, will sell out but how soon. The bill, announced today, closely tracks the conceptual, downbeat arc that indie-pop is on with The Decemberists headlining, preceded by Calexico, those wildly eclectic southwest psychedelics, with the local pop-rockers Solid Gold opening. So how can you assure yourself of a ticket–and at a real discount? Easy–members of Minnesota Public Radio or the Walker Art Center get an exclusive crack at tickets now through April 17. And if you become a new member of either org, you can receive one free ticket when joining or contributing at the $60 level; renewing or joining members at the $150 level can receive two tix. Here’s how: call or click the Walker at 612-375-7600 to join; call or click MPR at 1-800-227-2811 to join.