We work with numerous clients who are in high competition markets,

We see negative SEO attacks all the time, the thing is most of them do nothing to harm. One negative SEO attack I have seen were for a VC funded client I have in the US where they do time delayed attacks on numerous internal URLS (can be very annoying) I noticed most of my higher end affiliate clients get hit with negative SEO, corporate branded sites are less likely to be hit but it is good to monitor your link profile.  

What do these negative SEO attacks usually include?

- Usually they hit your websites landing page with 1000's of low quality links on exact match terms to specific landing pages they want to target.

- I have seen other cases where they may hit your site with 1000's of porn links, or links from the wrong type of neighborhood. If you have a clean site you do not want to be associated with those types of links.

What can you do to stop it?

The best thing you can do is:
1. Monitor your link profile during the week using software such as Ahrefs or Majesitc SEO (Paid) or Google Webmaster Tools link data, if something pops up which is not natural and of a negative natural.

2. Use the disavow tool and block the root file of the domain it is not that hard to do.:

https://support.google.com/webmasters/answer/2648487?hl=en

3. Their are other tactics you can do like 404ing domains and play around with re directs but to be honest the disavow tactic works well to stop this junk. In my eyes Google can probably see an attack as they hit the same market and same range of keywords.