Too long with one employer. How do you explain?

The labor market is getting faster and faster. The times when being employed at one employer for many years was appreciated are gone. Today, a CV looks much better when the applicant has changed employers at shorter intervals. Recruiters then immediately conclude that such candidates are more promising because they want to learn new things, explore new opportunities and seek new challenges.

When an applicant gets shortlisted with other candidates who are equally qualified, the length of the time he spent with one employer may disqualify him. Like candidates who change their jobs too often, candidates who stayed with former employers too long will have to defend their careers. What should they do?