A plot hole big enough for a Quidditch field

The Better Half and I saw the latest installment in the Harry Potter cinematic juggernaut this past weekend. He's read the entire series, whereas I still haven't finished the last book. Something about its steadily-increasing bleakness has kept me from enjoying the tail end of the series, though now I will probably just read it and be done with it. That said, Harry Potter and the Burgeoning Merchandise Deathly Hallows was worth the price of the sitter, despite large swaths being devoted to the three main characters sitting around moping and yelling at each other.

However, there is one gigantic plot hole that pops up right at the very end. As we were leaving the theater, I expressed my incredulity in no uncertain terms to the Better Half, who was unable to provide a satisfactory explanation.

At this point, please note the obligatory SPOILER ALERT. If you haven't seen the movie or read the book (or its prequel) and wish to do so unsullied by prior knowledge, stop now.

Still reading? Then help me understand something.

We spend the last bit of the movie watching Harry and Hermione try to figure out what a mysterious symbol means, and finally learn the secret of the titular Deathly Hallows. Apparently they're these three magical items, including a kick-ass wand. It turns out that Dumbledore was buried with it. The film ends with Voldemort wielding said wand to dramatic effect.

Now, I know that this is only Part I of Harry Potter and the Endless Franchise Deathly Hallows, so perhaps my question will be answered in Part II. However, if there were some immensely powerful wand that one might reasonably suspect the really powerful, evil wizard would want, maybe one might plan to protect it a wee bit better? Dumbledore obviously had the foresight to bequeath some handy items to Harry and Co. You'd think he'd have planned better than to hide the wand in his tomb, where bad guys might reasonably think to look and which is seemingly protected by nothing more than some really big rocks, easily moved by people who have such lucky gifts as magic powers.

At the end of the last film, we saw Harry and Dumbledore go after a magical locket, hidden in a remote cave in the middle of a zombie-infested lake and at the bottom of a cup of really nasty magical poison. Now that is how you hide something.

Maybe the Death Eaters aren't kicking ass and taking names because they're so much more powerful. Maybe they just take the time to think things through more.