A tip I've been using recently on my landscape photos that need a hard edge graduated ND filter is to use my hand. Yes my hand! I haven't purchased one because I've relied on Lightroom and photoshop to try to even out skies when I need too. But I am liking the result I'm getting by using my hand. Here is an example of when I use this technique.
You can see that the sky is totally blown out, too bright, compared to the log. Although the water looks very bright as well it is still less bright than the sky. A hard edge graduated ND filter here would be perfect to place along the edge of the water/treeline since its a hard edge already. I don't have one. So I used my hand as you can see in the video below. I leave my hand there for about a third of the exposure at first and then adjust from there. I normally do exposures over 30 seconds, but you can use this technique for shorter times as well.
I use the live view mode to position my hand and then an external remote to trigger the shutter. Of course you have to be careful not to bump the camera so your image will be sharp and you need a steady hand. But its a great thing to have in mind if you forget your filter or don't have one! I used this technique for the first image in this post and the few below. Happy shooting!