What should the spanish monarchs have done differently in order to have use the influx of silver to have increased their wealth for a longer period of time?

From the Spanish Empire in the New World came an influx of precious metals, which had profound economic effects. The flow became especially important in the second half of the sixteenth century, and consisted of both gold and silver, with the latter metal predominating. The Spanish went to great lengths to secure the entire supply for themselves and prevent any of their precious cargoes from falling into the hands of their rivals. Each year the plate fleet, bearing the bullion from the mines of Peru and Mexico, was accompanied to Spain by a convoy of warships, and during the sixteenth century no other nation ever succeeded in intercepting this fleet. Francis Drake was able, however, to rob Spanish treasure in Central America and in the Pacific.