Hello Bad design.
Thank you for reaching out to us. We are sorry to hear issue you are experiencing. The unit is not designed to stop when it near a pavement or wall. We would like to make some suggestions to improve your experience with the tool. Trimmer line usually breaks because of line crowding. This occurs when the trimmer head is held too close to hard objects that can break the line such as brick, cement, rocks, or fencing. Keeping the line at full extension, and not crowding it, reduces line breakage problems. We suggest cutting with the bare tip of the line because this is the section which moves at the highest speed. Do not let it hit into grass. Ease the line into vegetation, bit by bit from the edge. Line can also get wrapped around thick vegetation and become tangled, breaking the line. Listen to the sound of the machine and when the line slows down; back off out of the grass. We hope these suggestions help. If you still have questions or an unresolved issue after going through this troubleshooting guide, or just want to speak to a Greenworks product expert, please start a Live Chat on Greenworks Tools website or contact us by phone at 1-888-909-6757. We are here to help.