I'm pretty sure that is a stinkbug nymph. Stinkbugs are becoming a massive problem in home gardens and in agriculture and unfortunately insecticides are not very effective at controlling them. Here is a link to an earlier question about stinkbug control, there is lots of information in the answers which might be useful. Although it is talking about commercially grown plants, strategies like planting trap crops can be adapted to the home garden.
https://www.plantvillage.com/posts/67...
Is the insect in the picture moving or is it attached to the fence? We had a suggestion via facebook that it could be a ladybug larva and I realized that it might actually be a pupa (larva changing into an adult). almost 10 years ago.