Tarps, such as those for covering a truck or trailer, are usually made of rugged and durable material that is meant to withstand high winds, harsh rain, direct sunlight, and other inclement weather. However, this doesn't mean that the tarp is indestructible. After some years, the material weakens, and the tarp is likely to suffer rips and tears. Note a few quick tips for how to repair a tarp yourself, or why you want to leave it in the hands of a professional instead.
1. Construction adhesive
Construction adhesive is very durable as it holds together wood framing and other materials in a building. This makes it a good choice for holding together torn pieces of tarp of just about any material. You apply construction adhesive using a caulk gun, but note that you want to avoid cleaning up drips with your bare hands as it does dry quickly and is very difficult to remove from skin. The adhesive may also be too soft for use on a cloth tarp, but can hold together vinyl or PVC very easily.
2. Vinyl cement
Vinyl cement is a liquid glue or adhesive that is specifically meant for plugging up holes in any number of vinyl materials. This glue can be dabbed or spread onto a vinyl or PVC area and will easily hold together two sides of a tear; it's also fast-drying and watertight, so it's good for tarps used for covering construction materials during inclement weather. However, it also might be too soft for canvas tarps and is better just for vinyl or PVC.
Tarp tape is often found in auto supply or construction supply stores, and this can be used for a quick fix when you're on the road, or you can use duct tape. However, tape is not meant as a long-term fix, as it can easily come off at either end when exposed to high winds, and water from rain or snow can break down the adhesive. If you do use tape, apply it in an "H" shape, with a piece set vertically on each end of the rip and then a long piece set horizontally over its length, for maximum hold.
Canvas tarps are better repaired with a stitch job; this is often best left to a professional as it requires thread meant for upholstery or fabric and the use of heavy-duty sewing machines. A professional will also usually use thread glue under the thread to help hold it in place and keep the stitching permanent and secure.