Why did Qui-Gon and Anakin need to hide the fact that Anakin built the pod-racer?

Question

In Episode I, Anakin offered to pilot his pod-racer in the Boonta Eve and give the winnings to the Jedi and Queen Amidala. This would help them acquire the money they needed to repair Amidala's ship. However, when Anakin made this offer he told Qui-Gon

You could make [Watto] think [the pod-racer is] yours, and you could get him to let me pilot it for you.

_{script from Star Wars: Episode I The Phantom Menace}

Later, Qui-Gon lied to Watto and said he had acquired the pod-racer in a game of chance.

Why did Qui-Gon and Anakin need to deceive Watto about the fact that Anakin had built the pod-racer himself?

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Note: the idea for this question came from http://www.moviemistakes.com/film976/questions/page3.

Answer 1

Anakin is Watto's slave. Since Anakin's possessions are Watto's possessions, if Watto finds out that Anakin built the pod, then there's absolutely no reason why Watto would need to become partners with Qui-Gon for the use of a pod-racer that actually belongs to him in the first place.

“I’ve built a racer!” Anakin said. “It’s the fastest ever! There’s a big race the day after tomorrow — you could enter my Pod. It’s all but finished, and —”
“Anakin, settle down,” Shmi said. “Watto won’t let you —”
“Watto doesn’t know I’ve built it,” Anakin interrupted. He turned to Qui-Gon. “You could make him think it was yours, and you could get him to let me pilot for you.” - _{^{Phantom Menace: Junior Novelisation}}

At this point, Qui-Gon is basically gambling with Watto's own money

“I hope you didn’t kill anyone I know for it!” Watto snapped. He burst into a new round of laughter before bringing himself under control again. “So, you supply the Podracer and the entry fee; I supply the boy. We split the winnings fifty-fifty, I think.”
“Fifty-fifty?” Qui-Gon brushed the suggestion aside. “If it’s going to be fifty-fifty, I suggest you front the cost of the entry. If we win, you keep all the winnings, minus the cost of the parts I need. If we lose, you keep my ship.” - _{^{Phantom Menace: Official Novelisation}}