I don't know if anyone is interested in this article, but i use K2 as a Portfolio Component and there i had one problem, i don't want Google to follow the links when i add the URL in the Extra Field Links. 
Here is a Workaround so you can choose the rel tag nofollow in the dropdown:

Step 1:

Open the file: /administrator/components/com_k2/models/extrafields.php
around line 234 add this code:

$targetOptions[]=JHTML::_('select.option', 'nofollow', JText::_('No follow'));

Step 2:
Open the file: /administrator/components/com_k2/views/extrafield/tmpl/default.php
around line 125 add this code:

var option = new Element('option',{'value':'nofollow'}).setHTML('<?php echo JText::_('No Follow', true); ?>').injectInside(select);

and around line 142 add this code:

options[4] = new Element('option',{'value':'nofollow'}).setHTML('<?php echo JText::_('No Follow', true); ?>').injectInside(select);

Step 3:

Open the file: /components/com_k2/models/item.php

around line 879 add this code:

case 'nofollow':
$attributes='rel="nofollow"';
break;


DONE.

SEE THE SCREENSHOTS FOR FURTHER DETAILS.

Now you can choose in Extra Fields the nofollow in the Link Dropdown.

Thank you for the tip. But it would be better if there was a way to use the "nofollow" with tha option of opening the link always in a new window (not in the same, because the visitors are living the site) !!

 

Thank you anyway! It was very good!

in step 3 add:  

$attributes='rel="nofollow" target="_blank"'; 

instead of $attributes='rel="nofollow"';


this should work

 


Dimitris Trikkas said:

Thank you for the tip. But it would be better if there was a way to use the "nofollow" with tha option of opening the link always in a new window (not in the same, because the visitors are living the site) !!

 

Thank you anyway! It was very good!

Step 1:
Open the file: /administrator/components/com_k2/models/extrafields.php

 

change extrafields.php to extrafield.php 

 

 

Thank you very much for good instruction. It's work!

Anyone know how to do this on K2 ver. 2.5.4?

On step 2, it must be
<script>var option = new Element('option',{'value':'nofollow'}).setHTML('<?php echo JText::_('No Follow', true); ?>').injectInside(select);</script>
and
<script>options[4] = new Element('option',{'value':'nofollow'}).setHTML('<?php echo JText::_('No Follow', true); ?>').injectInside(select);</script>
Also, in K2 v8 step 3 is around line 1537.

Anyway, many thanks for that workaround! Great job!

This is a really old post but nice to hear that these solution still apply.
You can also render each field separately so you can have the markup you want.