I am pretty new to tikiwiki and was trying to implement adsense and adwords. I saw that there are many workarounds offered, but I tried a few and they didn't work for me. Also, there is much complaining about the lack of native implementation for these two popular features. I think I made some mistakes not knowing that much about tikiwiki. Also, some of the solutions were missing key details. Here is a step by step method to easily implement both of them. You don't need modules, templates, or any of that.
1) Log in as admin. Go to Admin >> look and feel>> General Layout.
2) Scroll down to custom site footer and click 'activate.' In the footer, copy your adsense and adwords script. Make sure you put {literal} SCRIPT {/literal}. The {literal} tag will prevent your script from being stripped out.