Today, I finally activated Sparky, my three-legged robotic dog. He is supposed to run on a ten-hour battery charge, but he immediately ran outside and started chasing fast-moving delivery trucks. Now I have to write an apology letter for my neighbor's highly damaged garden gnome!

three-legged: Compound adjectives made of a number and a noun (often with an "-ed" ending) are hyphenated before a noun.

ten-hour: When a number and a noun form an adjective before another noun, the noun in the compound is always singular and hyphenated (e.g., a ten-hour charge, NOT a ten-hours charge).

fast-moving: Adjective + participle combinations are hyphenated when they come directly before the noun they modify.

highly damaged: Never use a hyphen after an adverb ending in "-ly."