A safe alternative for getting rid of slugs is to use diatomaceous earth. This natural substance consists of fossilized skeletons of marine and freshwater organisms crushed into a powder of tiny glasslike pieces. When slugs get it on their bodies, they lose water rapidly, dry up and die. It also repels them because they try to avoid contact. This must be reapplied after every rainfall. Also, try to avoid watering at night, as this encourages the slug population.
If you want to make your own natural bug spray for general use in your garden, here's a recipe I've tried. It was fairly effective, but had to be reapplied frequently. The pepper's the deterrent; the soap makes it stick to the plants.
All-Purpose Bug Spray
2 tablespoons of liquid hot pepper
Few drops of liquid soap
1 spray bottle
ADD pepper and soap to water bottle. Fill with water. Let stand 24 hours. Shake and spray.
Other bug sprays use canola oil or mineral oil. Instead of hot pepper, you can try chopped garlic. When adding chopped garlic, the spray will need to be strained before use to remove the garlic. A baking soda and water formula can be sprayed on plants with fungal disease and a diluted milk solution helps with powdery mildew.