The local fly and tackle shop takes in rod repairs for me and the majority of them are for the replacement of damaged guides. I often wonder if the rod owners day of fishing ended unnecessarily when the guide was damaged.
Sometimes you can bend the guide back near original shape if it is not bent to badly. Other times the guide maybe smashed beyond straightening or the wire frame actually broke. Maybe the insert on your casting or spinning guide cracked or fell out. Now what? No back up rod. Is fishing over for the day? No way. All you need is a pocket knife, a replacement guide, and some electrical tape.
If your lucky the guide may have just came loose from the wrap that holds it on the rod. All you need to do is wrap the guide with some electrical tape to hold it in place. Electrical tape is made to stretch, so stretch it to get a tight wrap or your guide will come loose.
If the guide needs to be replaced. Take a pocket knife and shave the thread and finish off that hold the guide on the rod. The best way to do this is to start your cut on top of and near the end of the guide foot. Draw the knife toward the ring of the guide to shave off the thread and epoxy. It should go without saying, but take care not to cut yourself. Shave off a little at a time until you figure out how much you can take off safely. If you have a lighter you can heat the wrap a little and it will come off much easier. Also take care not to nick the rod with the knife. This is why you make the cut on top of the guide foot. It will protect the rod when your cutting. There will be several wraps beyond the guide foot that you need to take care on. You want to cut through the wraps without nicking the rod. If you can expose a thread and get hold of it a lot of the time you can unwrap the thread. The finish may flake off as your go. Sometimes you can peal it off with your fingernail.
Once you have the old guide and wraps off all you need to do is tape the new guide on tightly. A lot of the time the size and type of guide you use is not critical. Most anything will work. Having a few guides on hand in your tackle, boat, or vehicle should suffice. For double foot guides wrap both feet with tape. For single foot guides you will need to wrap tape on the foot and in front of the guide to lock it in place.
So don't let a damaged guide slow you down. A few simple items and a little know how will get you fishing again until you can have that rod repaired.