feet of lead is incorrectly written, and should be written as "with feet of lead" being its meaning:
Adverbial phrase used figurative and familiarly with the verb go or walk to mean proceed with caution and care either because of the importance of what is brought in hands or by the consequences of the matter or to avoid any trouble. They said some in 1969, when the Americans reached the Moon, astronauts landed with feet of lead, and not just figuratively, to better adapt to the gravity of the Moon, which is smaller than the Earth.
