If "slough" refers to the process of shedding skin:
* Retain: To keep or hold on to something.
* Keep: To maintain possession of something.
* Preserve: To keep something from being lost or damaged.
If "slough" refers to a swampy area:
* Upland: High ground, often dry and elevated.
* Dry land: Land that is not covered in water.
* Ridge: A long, narrow elevation of land.
* Plateau: An elevated, flat area of land.
If "slough" refers to a state of moral or physical decay:
* Flourish: To thrive or prosper.
* Thrive: To grow or develop vigorously.
* Prosper: To succeed in life, especially financially.
* Regenerate: To restore to a former state.
It's important to consider the specific context to determine the most appropriate antonym for "slough."