By defauly unity does autohide and sometimes this is ver annoying you can disable using the following procedure
First you need to install CompizConfig Settings Manager package using the following command from your terminal
sudo apt-get install compizconfig-settings-manager
Once installed, open the settings manager and scroll down until you see the ‘Ubuntu Unity Plugin' which is located in the Desktop category.
Now you need to set hide launcher option Set to ‘Never'.
The new settings will have automatically applied and the launcher will now be locked in place