This link show's you how to fix a hole in your yak, plastic welding.
There are plenty of write ups on the topic, however a video reference is always good. So, if you ever have a need for a DIY repair, the video will hopefully help.
http://www.teamoceankayak.com/videos/weld/index.html
Tools needed:
Repair/patch plastic (Old pickle buckets make good material)
Dremel
Sauteing Iron