If your neighbours can look you in the eye over your fence, you may need to add some height to the fence. Nothing personal against the neighbours, but maybe you don't want them watching your family cavort around in the swimming pool, or you hope to keep pets in more effectively with a taller fence. You have ways to add height to a fence, but most of them require money and muscles.
Several groups that discourage keeping dogs chained in back gardens have come up with suggestions for adding mesh fencing material to the top of an existing fence, thus adding height to a fence and hopefully thwarting Fido from jumping over the fence. Sometimes called "hardware cloth," this product comes in rolls of varying thicknesses. Choose one of the sturdier hardware cloths, and use wire ties to attach them to chain link fences.
Look for flexible fences made of plastic derivatives that are sold at hardware stores or online. Size 7.5 m (25 feet) long by 60 cm (2 feet) high and made of plastic, key phrases to look for include "hardware net" and "utility net." Even "poultry fence" netting, with its hexagonal shapes, can be used to make an existing fence higher. These are lightweight and primarily act as extra deterrents to keep things out of a fenced area. Use zip ties to attach.
Two kinds of lattice
Sections of wood lattice, framed and attached to the top of a fence, look good after they have been installed. However, wood lattice tends to sag after a while and pieces fall off due to harsh weather, and pretty soon you have a fence that doesn't look so good. Get a professional to install wood lattice fence toppers for the best appearance. This is no small job, so it will not be cheap. Also consider lattice fence toppers made with polyproylene, a hardy plastic. This product has a wood-grain appearance and is weather resistant. You can install it yourself with good results, but the labour is physically demanding work.
Foliage as a fence topper
If you have room to do so, plant foliage next to short fences. Choose a shrub that grows very quickly in your specific area. In a few years, quick-growing plants could easily extend above a fence, adding privacy. Bamboo grows very quickly - not only up, but it also grows out, encompassing ground rapidly. Use bamboo with caution. Virburnum and wax myrtle shrubs are evergreen and grow medium-fast.
Tips and warnings
Don't forget to consult your neighbours about changes to a boundary fence. Check on your deeds whether you actually own the fence. If you are in a conservation area or if your property or that of your neighbour is listed you will have additional planning requirements to deal with.