How do I permanently block someone on Twitter?

[:]]

On my Twitter, the same person follows me, its someone disgusted with a women sucking a mans penis as their picture, and on there page it has links to porn websites - disgusting.
When I report and block they come back and follow me again.
How do I permanently block this person from following me?

[Tom]

Oh my gosh. This exact thing happens to me! Just keep reporting them as spam, it's underneath the block option. They have stopped on mine now.