If you’re seeking a harder spanking, you should read this post on Newton’s 2nd Law, and how it pertains to spanking.
For more mass, use a heavier implement, like a thick paddle or wooden hairbrush.
For more acceleration, use something lighter, thinner and stingier, like a cane or a crop, as explained in this post.
But fundamentally, I don’t consider a physical marks and bruises to be the most desirable outcome from a spanking. I believe the aim should be achieving a deep psychological satisfaction, better to wake in the morning with a clear mind and some great memories, than with a sore bottom and a frustrated head.
I know good disciplinarians are very rare. So if you’re not lucky enough to have one, do try exploring by yourself, remember there’s more to a spanking than physical pain, and that every spanking is experienced not by the buttocks, but by the awesomely sophisticated region between your ears…