Are you using playground sand or one of the larger grain size sands that tend to get stuck in impeller shafts? I use Estes aquarium sdands which are small enough that any sand that gets pulled in is small enough to get pushed by the impeller and back out into the body. Out of over 100 Marineland filters since the mid 90's I've never had to replace one or even an impeller for that matter.
If you're collecting sand it sounds like you have the intake a little too low to the bottom. The Marineland filters can have their intake tubes shortened about an inch at a time easily until you find the height that gives you the best collection but not close enough to pull up the sand.
Another option used to be adding a simple prefilter sponge.
http://www.aquacave.com/detail.aspx?ID=789
I've used the brand pictured there many times. They offer 3 sizes through many retailers. They used to have a variety of adapters to fit all the Whispers and Penguin filters but Marineland recently changed the intake tube to a rectangular design so they may not directly adapt anymore. They should still fit the Whispers though and I could DIY a similar version to fit the rectangular intake tubes of the Marineland filters if needed. As a side benefit they eliminate the need to purchase replacement cartridges for mechanical filtration since the sponge now serves as your mechanical media. You get some bio ability also.
For refilling tanks I use a garden hose with an inline shutoff availible at most hardware stores. A whisper Jr strainer fits into the end of most of them securely which forces the water coming out of the hose to exit sideways taking away the force that can splash sand around and aerating nicely at the same time which helps if you have chlorine. Here's a picture of what it looks like and a simple modification to any gravel vac for working sand tanks.
http://i140.photobucket.com/albums/r.../gravelvac.jpg 
Sand In My Power Filter 
