I tried three different sites for link development and two
of them monitor the process and you approve the links through their site. This gives you some control on who links to you.

The third site I submitted to did not have a lot of requirements and it did allow you to specify the type of sites you would accept links from.

I have since found that some pretty awful sites (porn) have linked to my site. I found them by checking my Alexa rating and found the sites that were linking to mine. I have been trying to block them ever since. My hosting website suggested that I add a script that blocks them.

If anyone has any suggestions on to stop this it would be helpful.

So to answer your question, be careful.