Non line of sight feasibility
Dog legging is when both ends of the link have not got line of sight to each other, but both have line of sight to a common point. This common point can be used as an intermediate point or "dog leg". The most efficient way to use this point is to have 2 separate wireless bridges (4 radios total) as there is no loss of throughput. It is possible also to create a dog leg by having the intermediate point repeat the signal however this will half the links throughput as the central radio has to spend half its time listening to signals sent to it, and the other repeating them.
Using a Lower Frequency
Lower frequencies have longer wavelengths so are less prone to the effects of attenuation. A great example of this when you look at Dual band access points inside buildings. If you take a reading in the next room you will see that the 2.4GHz signal is stronger than the 5GHz (in most cases). This is because the shorter wavelength of the 5GHz signal is effected more by the walls than the 2.4GHz. For this reason, high frequency microwave links such as 60 and 80GHz require perfect line of sight, whereas 5GHz links can often punch through trees and bushes etc. If your 5GHz link is not working then a 2.4GHz may be the answer.
Raise The Output Power
The higher the output power, the more likely the signal is to penetrate any obstacles. You need to be careful to operate within legal limits however if you take 5GHz as an example then if operating in band B you can only output at 1W. If this is not enough then moving to operate in band C will allow you to output at 4W which may solve your problem.
Physically Mount the link higher
The simplest way to achieve line of site in a lot of cases is to mount your wireless equipment on the top of large poles. The pole must be properly mounted and guided down to prevent movement.
Multipath is your friend
In some cases it may be possible to use surrounding buildings or reflective surfaces to bounce the wireless signal around corners or obstacles. This can be a bit hit and miss and result in low data rates, but I have seen a fair number of links use this method and work fine.
In short, just because you don't have line of sight, it doesn\'t mean a link cant be achieved but until you actually survey the link using the correct hardware you are not going to know for sure. Use caution in situations where the environment can change. For example if you have a link that goes through trees and works well during the winter, that same link may not work during the summer when the trees are in bloom!