How do I ensure a model always uses a transaction and locks (in Rails)?

I noticed that Rails can have concurrency issues with multiple servers and would like to force my model to always lock. Is this possible in Rails, similar to unique constraints to force data integrity? Or does it just require careful programming?

Terminal One

irb(main):033:0* Vote.transaction do
irb(main):034:1* v = Vote.lock.first
irb(main):035:1> v.vote += 1
irb(main):036:1> sleep 60
irb(main):037:1> v.save
irb(main):038:1> end

Terminal Two, while sleeping

irb(main):240:0* Vote.transaction do
irb(main):241:1* v = Vote.first
irb(main):242:1> v.vote += 1
irb(main):243:1> v.save
irb(main):244:1> end

DB Start

 select * from votes where id = 1;
 id | vote |         created_at         |         updated_at         
----+------+----------------------------+----------------------------
  1 |    0 | 2013-09-30 02:29:28.740377 | 2013-12-28 20:42:58.875973 

After execution

Terminal One

irb(main):040:0> v.vote
=> 1

Terminal Two

irb(main):245:0> v.vote
=> 1

DB End

select * from votes where id = 1;
 id | vote |         created_at         |         updated_at         
----+------+----------------------------+----------------------------
  1 |    1 | 2013-09-30 02:29:28.740377 | 2013-12-28 20:44:10.276601 

Other Example

http://rhnh.net/2010/06/30/acts-as-list-will-break-in-production