The jewelry store is well-guarded with professional security personnel around the clock.

well-guarded 是由副词 well（好地）和动词 guard（守卫、保护）的过去分词 guarded 组成的复合形容词。well 表示程度，guarded 表示被动状态，合起来意思是"被很好地保护着的"。 around the clock 是固定短语，clock 指"时钟"，字面意思是"围绕着时钟"，引申为"24小时不间断地"。