Intrepid trail riders won't let a little rain or soggy footing keep them at home. And it's perfectly safe to ride at reasonable speeds through wet and even sloppy footing. But deep mud can present problems, ranging from the nuisance of a pulled shoe to the true emergency of a stuck horse. Knowing how to handle muddy going to minimize risks is an essential skill of all-weather trail riders.
After a heavy rain, stick to well-maintained roads and trails you are familiar with. Now is not the time to go exploring. If you come across a questionable area, look for deer tracks in the mud that will help you judge how deep it is. If you must cross muddy ground, allow your horse to choose the route, keeping the rein loose so he can easily maintain his balance. If he is normally willing to walk through mucky footing but suddenly objects, he may see or sense something you can't, and it is wise to pick a different path.
If your horse does start to slip or flounder in the mud, gently urge him toward solid footing. Horses have a natural tendency to seek firm ground, so he'll most likely be one step ahead of you. However, if he begins to sink or seems unable to move, quickly and calmly dismount and let go of the reins. Most horses can free themselves from boggy situations, but if yours can't, he'll quickly stop struggling and be still. That is your cue to seek help. Send another rider back or call out for help from passersby. You'll need a veterinarian and possibly emergency rescue personnel if your horse needs to be pulled free.