There are rough patches in training and during races. Mentally enduring during training should help you during races.
Walking is one alternative many promote and employ to overcome rough patches. I believe in walking some during marathons to regain energy. I also like to run backwards. Running backwards allows me to maintain my pace while giving my hamstrings and other forward thrusting muscles a break. My first marathon I ran the entire distance, hit the wall hard at 23 miles and came up short on qualifying for Boston. In my next 2 marathons (both yielding Boston qualifying times) I walked and ran backward. The wall never appeared in those races.
One other technic many forget about is actually speeding up when tired. It may seem counterintuitive yet the difference in cadence will revive you and help propel you on.
Many marathons promote a fast flat course. Sometimes the lack of hills forces you to get creative to not overwork the same muscles over and over again. Using the methods listed above will help add needed variety to your pace and allow you perform better.