I use WidgetLocker. It allows you to set a different wallpaper for your lockscreen, place widgets on there as well, AND has a setting so you would need to unlock the screen before answering or ignoring the call. I used to do it too, until I set this up.
Some people don't like having to unlock this app, plus the stock slider and pin/password/pattern, but I disabled the stock one. (Don't ask me how I did it, I just have that option, but it doesn't seem like everyone does!)