Doner, one of Detroit \'s largest ad agencies, has lost Circuit City Stores Inc. as a client -- the second account to slip away from it in as many weeks. The Southfield-based company had been the agency of record for the nation\'s second-largest consumer-electronics retailer since 2004. It said its contract with Circuit City ended at the end of February and wasn\'t renewed. \"Without a doubt, it\'s important to try to hold onto existing accounts,\" said Jeff Stoltman, a marketing professor at Wayne State University . \"You do start to get some morale issues that pop up in an agency when you lose a couple of key accounts, but I\'m sure Doner management is on the case.\"