뼈가 삭다 = 뼈가 약해지다 means "have weak bones" 그만해라 뼈 삭는다 means Stop doing that unless you will have weak bones. (Used as an excuse to prohibit some bad habits)

You should guess the meaning from context. 뻐가 삭다, 골병이 들다, 겉으로는 멀쩡하지만 속으로는 병이 들거나 상처를 입다.