**Rosin/Pine sap.** 

I remembered that baseball players sometimes use rosin in their gloves to keep the baseball from slipping out. 
```
"Rosin, also known as colophony, is the sap or sticky substance that comes from pine and spruce trees.
 Its stickiness lends itself to being used in a wide range of products."
```
[source][1]

So I went over to a grove of pine trees, pulled off a clump of sap on the side, and rubbed it on the pulleys and belt of my mower. Then, to clean my hands off I had to use another trick: I rubbed my hands in vegetable oil until the sap mixed with the oil. Then I washed it all off with normal hand-soap. The belt hasn't slipped yet!! And now I can mow through taller grass at full-speed. It works great.

  [1]: https://dermnetnz.org/topics/rosin-allergy/