In Half-Blood Prince, Dumbledore and Harry have this exchange right after they enter the cave and just before crossing the lake that would get them to the Horcrux Island where the Drink of Despair was located.

This is what is written:

Immediately a thick coppery green chain appeared out of thin air, extending from the depths of the water into Dumbledore’s clenched hand. Dumbledore tapped the chain, which began to slide through his fist like a snake, coiling itself on the ground with a clinking sound that echoed noisily off the rocky walls, pulling something from the depths of the black water. Harry gasped as the ghostly prow of a tiny boat broke the surface, glowing as green as the chain, and floated, with barely a ripple, toward the place on the bank where Harry and Dumbledore stood.

“How did you know that was there?” Harry asked in astonishment.

“Magic always leaves traces,” said Dumbledore, as the boat hit the bank with a gentle bump, “sometimes very distinctive traces. I taught Tom Riddle. I know his style.”

“Is…is this boat safe?”

“Oh yes, I think so. Voldemort needed to create a means to cross the lake without attracting the wrath of those creatures he had placed within it in case he ever wanted to visit or remove his Horcrux.”

“So the things in the water won’t do anything to us if we cross in Voldemort’s boat?”

“I think we must resign ourselves to the fact that they will, at some point, realize we are not Lord Voldemort. Thus far, however, we have done well. They have allowed us to raise the boat.”

Right in the bolded text, Dumbledore says that Voldemort needed to create a means to cross the lake without attracting the wrath of the Inferi in case he ever wanted to check on the status of the Horcrux.

Does that imply that Voldemort could NOT control the Inferi?
How then did Voldemort enchant the Inferi to defend the Horcrux in the first place?