Safely calling other plugin code from a different plugin
You could write a wrapper log method that's abstracts the check away so you only have to do it once.  The update your code to use the wrapper.

That method could just use craft()-&gt;plugins-&gt;getPlugin('pluginHandle') to see if the target plugin is installed and enabled.  Craft will auto-load the plugin's services, so you don't need to check specifically for them.