Deterring garden pests need not be expensive. This can be done cheaply and humanely using one of the methods below.
Deterring slugs and snails with food waste or used glass and copper
Instead of purchasing slug pellets to poison these pests, simply use a ring of coffee grounds around your precious plants to deter them. Slugs and snails hate the smell of coffee grounds and the chemicals they contain, however ground coffee is good for your plants as it contains nitrogen, potassium and phosphorus - so this is a win win situation. Copper also deters slugs and snails; a used copper wire from a defunct electrical item will create an effective barrier against slimy invasions. Finally, a sharp 'wall' of broken glass around your flower beds will cause slugs and snails to recoil in horror when they attempt to enter them; just make sure that this will not pose a danger to children, pets or human visitors to your garden.
Deterring birds with recycled tin foil
Old foil tins, of the kind that are used to hold shop bought pies, can be hung from branches or staves to scare away birds from your fruit trees or vegetable plot. The sound of these tins in the wind, as well as the way that they flash as they reflect the sun's light, will prove a powerful deterrent to all kinds of birds.
Deterring moles by attracting owls or deploying planted borders
Calling out pest control to trap moles in your garden can cost hundreds of pounds. In the spring time, moles can be deterred naturally with a planted border of daffodils in areas of your garden that are frequented by moles (or close to mole hills in neighbouring fields or gardens). Moles are repelled by daffodils, and the good news is that if you plant daffodil bulbs one year, this low maintenance plant will continue flowering in subsequent springs without you needing to do anything. Marigolds and castor plants provide similar mole repelling barriers. Castor oil itself is an inexpensive mole repellent. Mixed with water, and sprinkled on the soil, it will cause moles to seek a new home in disgust. Castor plants, castor oil and marigolds are poisonous to pets and children, however. Owls are another known mole deterrent; building an owl box in your garden will often be all you need to do to ensure that you have a constant feathered guard looking after your garden. Attempting to mix your own poisons from harmful substances in order to kill moles is definitely not recommended - improper use of poisons is not only cruel to moles (and may lead to a visit from the RSPCA), but it can also irreparably damage the fertility of your soil and kill your plants.
The right deterrents are lying around your home right now
Scoop those coffee grounds from the pot, save those old pie cases and grab some cheap daffodil bulbs from the supermarket. Garden pests will be gone in no time.