Safe Site with URL forwarding Service

Our web site uses a URL forwarding service (www.dyndns.com).  The actual site IP address shows as safe but, when we access through the forwarding servies it shows as unsafe.  The URL is:  http://k5ozk.ham-radio-op.net/ or www.k5ozk.ham-radio-op.net/.  Why does this happen and how can we eliminate the Unsafe Site message?