We had our interlocking at the side of the house done by Concord two summers ago-in 2008 (with warranty). After a year the stones close to the retaining wall started to cave in (sinking). We called several time last summer to fix the problem, Mike the salesman came over and said they will send someone to fix it. No one came. This year we started calling the company in Spring about the problem which now become worse, they keep on saying they will send someone to look and fix the it. Until now we are still waiting for the guys that the company is going to send to fix our interlocking.
Concord is not a very reliable company, do not give them your business.