for a coon's age
For an exceptionally long period of time. Based on the folk belief that raccoons (shortened colloquially to "coons") have a longer-than-average lifespan. I could work on this project for a coon's age, and I still wouldn't get it all done! I haven't been on a vacation for a coon's age.
for (or in) a coon's age
a very long time. North American informal 1951 William Styron Lie Down in Darkness I haven't seen him in a coon's age.